linux/drivers/i2c/i2c-mux.c

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/*
* Multiplexed I2C bus driver.
*
* Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
* Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
* Copyright (c) 2009-2010 NSN GmbH & Co KG <michael.lawnick.ext@nsn.com>
*
* Simplifies access to complex multiplexed I2C bus topologies, by presenting
* each multiplexed bus segment as an additional I2C adapter.
* Supports multi-level mux'ing (mux behind a mux).
*
* Based on:
* i2c-virt.c from Kumar Gala <galak@kernel.crashing.org>
* i2c-virtual.c from Ken Harrenstien, Copyright (c) 2004 Google, Inc.
* i2c-virtual.c from Brian Kuschak <bkuschak@yahoo.com>
*
* This file is licensed under the terms of the GNU General Public
* License version 2. This program is licensed "as is" without any
* warranty of any kind, whether express or implied.
*/
#include <linux/acpi.h>
#include <linux/i2c.h>
#include <linux/i2c-mux.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/slab.h>
/* multiplexer per channel data */
struct i2c_mux_priv {
struct i2c_adapter adap;
struct i2c_algorithm algo;
struct i2c_mux_core *muxc;
u32 chan_id;
};
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
static int __i2c_mux_master_xfer(struct i2c_adapter *adap,
struct i2c_msg msgs[], int num)
{
struct i2c_mux_priv *priv = adap->algo_data;
struct i2c_mux_core *muxc = priv->muxc;
struct i2c_adapter *parent = muxc->parent;
int ret;
/* Switch to the right mux port and perform the transfer. */
ret = muxc->select(muxc, priv->chan_id);
if (ret >= 0)
ret = __i2c_transfer(parent, msgs, num);
if (muxc->deselect)
muxc->deselect(muxc, priv->chan_id);
return ret;
}
static int i2c_mux_master_xfer(struct i2c_adapter *adap,
struct i2c_msg msgs[], int num)
{
struct i2c_mux_priv *priv = adap->algo_data;
struct i2c_mux_core *muxc = priv->muxc;
struct i2c_adapter *parent = muxc->parent;
int ret;
/* Switch to the right mux port and perform the transfer. */
ret = muxc->select(muxc, priv->chan_id);
if (ret >= 0)
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
ret = i2c_transfer(parent, msgs, num);
if (muxc->deselect)
muxc->deselect(muxc, priv->chan_id);
return ret;
}
static int __i2c_mux_smbus_xfer(struct i2c_adapter *adap,
u16 addr, unsigned short flags,
char read_write, u8 command,
int size, union i2c_smbus_data *data)
{
struct i2c_mux_priv *priv = adap->algo_data;
struct i2c_mux_core *muxc = priv->muxc;
struct i2c_adapter *parent = muxc->parent;
int ret;
/* Select the right mux port and perform the transfer. */
ret = muxc->select(muxc, priv->chan_id);
if (ret >= 0)
ret = __i2c_smbus_xfer(parent, addr, flags,
read_write, command, size, data);
if (muxc->deselect)
muxc->deselect(muxc, priv->chan_id);
return ret;
}
static int i2c_mux_smbus_xfer(struct i2c_adapter *adap,
u16 addr, unsigned short flags,
char read_write, u8 command,
int size, union i2c_smbus_data *data)
{
struct i2c_mux_priv *priv = adap->algo_data;
struct i2c_mux_core *muxc = priv->muxc;
struct i2c_adapter *parent = muxc->parent;
int ret;
/* Select the right mux port and perform the transfer. */
ret = muxc->select(muxc, priv->chan_id);
if (ret >= 0)
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
ret = i2c_smbus_xfer(parent, addr, flags,
read_write, command, size, data);
if (muxc->deselect)
muxc->deselect(muxc, priv->chan_id);
return ret;
}
/* Return the parent's functionality */
static u32 i2c_mux_functionality(struct i2c_adapter *adap)
{
struct i2c_mux_priv *priv = adap->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
return parent->algo->functionality(parent);
}
/* Return all parent classes, merged */
static unsigned int i2c_mux_parent_classes(struct i2c_adapter *parent)
{
unsigned int class = 0;
do {
class |= parent->class;
parent = i2c_parent_is_i2c_adapter(parent);
} while (parent);
return class;
}
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
static void i2c_mux_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
i2c/mux, locking/core: Annotate the nested rt_mutex usage If an i2c topology has instances of nested muxes, then a lockdep splat is produced when when i2c_parent_lock_bus() is called. Here is an example: ============================================ WARNING: possible recursive locking detected -------------------------------------------- insmod/68159 is trying to acquire lock: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] but task is already holding lock: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(i2c_register_adapter#2); lock(i2c_register_adapter#2); *** DEADLOCK *** May be due to missing lock nesting notation 1 lock held by insmod/68159: #0: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] stack backtrace: CPU: 13 PID: 68159 Comm: insmod Tainted: G O Call Trace: dump_stack+0x67/0x98 __lock_acquire+0x162e/0x1780 lock_acquire+0xba/0x200 rt_mutex_lock+0x44/0x60 i2c_parent_lock_bus+0x32/0x50 [i2c_mux] i2c_parent_lock_bus+0x3e/0x50 [i2c_mux] i2c_smbus_xfer+0xf0/0x700 i2c_smbus_read_byte+0x42/0x70 my2c_init+0xa2/0x1000 [my2c] do_one_initcall+0x51/0x192 do_init_module+0x62/0x216 load_module+0x20f9/0x2b50 SYSC_init_module+0x19a/0x1c0 SyS_init_module+0xe/0x10 do_syscall_64+0x6c/0x1a0 entry_SYSCALL_64_after_hwframe+0x42/0xb7 Reported-by: John Sperbeck <jsperbeck@google.com> Tested-by: John Sperbeck <jsperbeck@google.com> Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Deepa Dinamani <deepadinamani@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Chang <dpf@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: Wolfram Sang <wsa@the-dreams.de> Link: http://lkml.kernel.org/r/20180720083914.1950-3-peda@axentia.se Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-20 08:39:14 +00:00
rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
if (!(flags & I2C_LOCK_ROOT_ADAPTER))
return;
i2c_lock_bus(parent, flags);
}
static int i2c_mux_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
if (!rt_mutex_trylock(&parent->mux_lock))
return 0; /* mux_lock not locked, failure */
if (!(flags & I2C_LOCK_ROOT_ADAPTER))
return 1; /* we only want mux_lock, success */
if (i2c_trylock_bus(parent, flags))
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
return 1; /* parent locked too, success */
rt_mutex_unlock(&parent->mux_lock);
return 0; /* parent not locked, failure */
}
static void i2c_mux_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
if (flags & I2C_LOCK_ROOT_ADAPTER)
i2c_unlock_bus(parent, flags);
rt_mutex_unlock(&parent->mux_lock);
}
static void i2c_parent_lock_bus(struct i2c_adapter *adapter,
unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
i2c/mux, locking/core: Annotate the nested rt_mutex usage If an i2c topology has instances of nested muxes, then a lockdep splat is produced when when i2c_parent_lock_bus() is called. Here is an example: ============================================ WARNING: possible recursive locking detected -------------------------------------------- insmod/68159 is trying to acquire lock: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] but task is already holding lock: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(i2c_register_adapter#2); lock(i2c_register_adapter#2); *** DEADLOCK *** May be due to missing lock nesting notation 1 lock held by insmod/68159: #0: (i2c_register_adapter#2){+.+.}, at: i2c_parent_lock_bus+0x32/0x50 [i2c_mux] stack backtrace: CPU: 13 PID: 68159 Comm: insmod Tainted: G O Call Trace: dump_stack+0x67/0x98 __lock_acquire+0x162e/0x1780 lock_acquire+0xba/0x200 rt_mutex_lock+0x44/0x60 i2c_parent_lock_bus+0x32/0x50 [i2c_mux] i2c_parent_lock_bus+0x3e/0x50 [i2c_mux] i2c_smbus_xfer+0xf0/0x700 i2c_smbus_read_byte+0x42/0x70 my2c_init+0xa2/0x1000 [my2c] do_one_initcall+0x51/0x192 do_init_module+0x62/0x216 load_module+0x20f9/0x2b50 SYSC_init_module+0x19a/0x1c0 SyS_init_module+0xe/0x10 do_syscall_64+0x6c/0x1a0 entry_SYSCALL_64_after_hwframe+0x42/0xb7 Reported-by: John Sperbeck <jsperbeck@google.com> Tested-by: John Sperbeck <jsperbeck@google.com> Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Deepa Dinamani <deepadinamani@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Chang <dpf@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Philippe Ombredanne <pombredanne@nexb.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: Wolfram Sang <wsa@the-dreams.de> Link: http://lkml.kernel.org/r/20180720083914.1950-3-peda@axentia.se Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-20 08:39:14 +00:00
rt_mutex_lock_nested(&parent->mux_lock, i2c_adapter_depth(adapter));
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
i2c_lock_bus(parent, flags);
}
static int i2c_parent_trylock_bus(struct i2c_adapter *adapter,
unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
if (!rt_mutex_trylock(&parent->mux_lock))
return 0; /* mux_lock not locked, failure */
if (i2c_trylock_bus(parent, flags))
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
return 1; /* parent locked too, success */
rt_mutex_unlock(&parent->mux_lock);
return 0; /* parent not locked, failure */
}
static void i2c_parent_unlock_bus(struct i2c_adapter *adapter,
unsigned int flags)
{
struct i2c_mux_priv *priv = adapter->algo_data;
struct i2c_adapter *parent = priv->muxc->parent;
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
i2c_unlock_bus(parent, flags);
rt_mutex_unlock(&parent->mux_lock);
}
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
struct i2c_adapter *i2c_root_adapter(struct device *dev)
{
struct device *i2c;
struct i2c_adapter *i2c_root;
/*
* Walk up the device tree to find an i2c adapter, indicating
* that this is an i2c client device. Check all ancestors to
* handle mfd devices etc.
*/
for (i2c = dev; i2c; i2c = i2c->parent) {
if (i2c->type == &i2c_adapter_type)
break;
}
if (!i2c)
return NULL;
/* Continue up the tree to find the root i2c adapter */
i2c_root = to_i2c_adapter(i2c);
while (i2c_parent_is_i2c_adapter(i2c_root))
i2c_root = i2c_parent_is_i2c_adapter(i2c_root);
return i2c_root;
}
EXPORT_SYMBOL_GPL(i2c_root_adapter);
struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
struct device *dev, int max_adapters,
int sizeof_priv, u32 flags,
int (*select)(struct i2c_mux_core *, u32),
int (*deselect)(struct i2c_mux_core *, u32))
{
struct i2c_mux_core *muxc;
muxc = devm_kzalloc(dev, sizeof(*muxc)
+ max_adapters * sizeof(muxc->adapter[0])
+ sizeof_priv, GFP_KERNEL);
if (!muxc)
return NULL;
if (sizeof_priv)
muxc->priv = &muxc->adapter[max_adapters];
muxc->parent = parent;
muxc->dev = dev;
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
if (flags & I2C_MUX_LOCKED)
muxc->mux_locked = true;
if (flags & I2C_MUX_ARBITRATOR)
muxc->arbitrator = true;
if (flags & I2C_MUX_GATE)
muxc->gate = true;
muxc->select = select;
muxc->deselect = deselect;
muxc->max_adapters = max_adapters;
return muxc;
}
EXPORT_SYMBOL_GPL(i2c_mux_alloc);
static const struct i2c_lock_operations i2c_mux_lock_ops = {
.lock_bus = i2c_mux_lock_bus,
.trylock_bus = i2c_mux_trylock_bus,
.unlock_bus = i2c_mux_unlock_bus,
};
static const struct i2c_lock_operations i2c_parent_lock_ops = {
.lock_bus = i2c_parent_lock_bus,
.trylock_bus = i2c_parent_trylock_bus,
.unlock_bus = i2c_parent_unlock_bus,
};
int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
u32 force_nr, u32 chan_id,
unsigned int class)
{
struct i2c_adapter *parent = muxc->parent;
struct i2c_mux_priv *priv;
char symlink_name[20];
int ret;
if (muxc->num_adapters >= muxc->max_adapters) {
dev_err(muxc->dev, "No room for more i2c-mux adapters\n");
return -EINVAL;
}
priv = kzalloc(sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
/* Set up private adapter data */
priv->muxc = muxc;
priv->chan_id = chan_id;
/* Need to do algo dynamically because we don't know ahead
* of time what sort of physical adapter we'll be dealing with.
*/
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
if (parent->algo->master_xfer) {
if (muxc->mux_locked)
priv->algo.master_xfer = i2c_mux_master_xfer;
else
priv->algo.master_xfer = __i2c_mux_master_xfer;
}
if (parent->algo->master_xfer_atomic)
priv->algo.master_xfer_atomic = priv->algo.master_xfer;
i2c: mux: relax locking of the top i2c adapter during mux-locked muxing With a i2c topology like the following GPIO ---| ------ BAT1 | v / I2C -----+----------+---- MUX | \ EEPROM ------ BAT2 there is a locking problem with the GPIO controller since it is a client on the same i2c bus that it muxes. Transfers to the mux clients (e.g. BAT1) will lock the whole i2c bus prior to attempting to switch the mux to the correct i2c segment. In the above case, the GPIO device is an I/O expander with an i2c interface, and since the GPIO subsystem knows nothing (and rightfully so) about the lockless needs of the i2c mux code, this results in a deadlock when the GPIO driver issues i2c transfers to modify the mux. So, observing that while it is needed to have the i2c bus locked during the actual MUX update in order to avoid random garbage on the slave side, it is not strictly a must to have it locked over the whole sequence of a full select-transfer-deselect mux client operation. The mux itself needs to be locked, so transfers to clients behind the mux are serialized, and the mux needs to be stable during all i2c traffic (otherwise individual mux slave segments might see garbage, or worse). Introduce this new locking concept as "mux-locked" muxes, and call the pre-existing mux locking scheme "parent-locked". Modify the i2c mux locking so that muxes that are "mux-locked" locks only the muxes on the parent adapter instead of the whole i2c bus when there is a transfer to the slave side of the mux. This lock serializes transfers to the slave side of the muxes on the parent adapter. Add code to i2c-mux-gpio and i2c-mux-pinctrl that checks if all involved gpio/pinctrl devices have a parent that is an i2c adapter in the same adapter tree that is muxed, and request a "mux-locked mux" if that is the case. Modify the select-transfer-deselect code for "mux-locked" muxes so that each of the select-transfer-deselect ops locks the mux parent adapter individually. Signed-off-by: Peter Rosin <peda@axentia.se> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-05-04 20:15:29 +00:00
if (parent->algo->smbus_xfer) {
if (muxc->mux_locked)
priv->algo.smbus_xfer = i2c_mux_smbus_xfer;
else
priv->algo.smbus_xfer = __i2c_mux_smbus_xfer;
}
if (parent->algo->smbus_xfer_atomic)
priv->algo.smbus_xfer_atomic = priv->algo.smbus_xfer;
priv->algo.functionality = i2c_mux_functionality;
/* Now fill out new adapter structure */
snprintf(priv->adap.name, sizeof(priv->adap.name),
"i2c-%d-mux (chan_id %d)", i2c_adapter_id(parent), chan_id);
priv->adap.owner = THIS_MODULE;
priv->adap.algo = &priv->algo;
priv->adap.algo_data = priv;
priv->adap.dev.parent = &parent->dev;
priv->adap.retries = parent->retries;
priv->adap.timeout = parent->timeout;
priv->adap.quirks = parent->quirks;
if (muxc->mux_locked)
priv->adap.lock_ops = &i2c_mux_lock_ops;
else
priv->adap.lock_ops = &i2c_parent_lock_ops;
/* Sanity check on class */
if (i2c_mux_parent_classes(parent) & class)
dev_err(&parent->dev,
"Segment %d behind mux can't share classes with ancestors\n",
chan_id);
else
priv->adap.class = class;
/*
* Try to populate the mux adapter's of_node, expands to
* nothing if !CONFIG_OF.
*/
if (muxc->dev->of_node) {
struct device_node *dev_node = muxc->dev->of_node;
struct device_node *mux_node, *child = NULL;
u32 reg;
if (muxc->arbitrator)
mux_node = of_get_child_by_name(dev_node, "i2c-arb");
else if (muxc->gate)
mux_node = of_get_child_by_name(dev_node, "i2c-gate");
else
mux_node = of_get_child_by_name(dev_node, "i2c-mux");
if (mux_node) {
/* A "reg" property indicates an old-style DT entry */
if (!of_property_read_u32(mux_node, "reg", &reg)) {
of_node_put(mux_node);
mux_node = NULL;
}
}
if (!mux_node)
mux_node = of_node_get(dev_node);
else if (muxc->arbitrator || muxc->gate)
child = of_node_get(mux_node);
if (!child) {
for_each_child_of_node(mux_node, child) {
ret = of_property_read_u32(child, "reg", &reg);
if (ret)
continue;
if (chan_id == reg)
break;
}
}
priv->adap.dev.of_node = child;
of_node_put(mux_node);
}
/*
* Associate the mux channel with an ACPI node.
*/
if (has_acpi_companion(muxc->dev))
acpi_preset_companion(&priv->adap.dev,
ACPI_COMPANION(muxc->dev),
chan_id);
if (force_nr) {
priv->adap.nr = force_nr;
ret = i2c_add_numbered_adapter(&priv->adap);
if (ret < 0) {
dev_err(&parent->dev,
"failed to add mux-adapter %u as bus %u (error=%d)\n",
chan_id, force_nr, ret);
goto err_free_priv;
}
} else {
ret = i2c_add_adapter(&priv->adap);
if (ret < 0) {
dev_err(&parent->dev,
"failed to add mux-adapter %u (error=%d)\n",
chan_id, ret);
goto err_free_priv;
}
}
WARN(sysfs_create_link(&priv->adap.dev.kobj, &muxc->dev->kobj,
"mux_device"),
"can't create symlink to mux device\n");
snprintf(symlink_name, sizeof(symlink_name), "channel-%u", chan_id);
WARN(sysfs_create_link(&muxc->dev->kobj, &priv->adap.dev.kobj,
symlink_name),
"can't create symlink to channel %u\n", chan_id);
dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
i2c_adapter_id(&priv->adap));
muxc->adapter[muxc->num_adapters++] = &priv->adap;
return 0;
err_free_priv:
kfree(priv);
return ret;
}
EXPORT_SYMBOL_GPL(i2c_mux_add_adapter);
void i2c_mux_del_adapters(struct i2c_mux_core *muxc)
{
char symlink_name[20];
while (muxc->num_adapters) {
struct i2c_adapter *adap = muxc->adapter[--muxc->num_adapters];
struct i2c_mux_priv *priv = adap->algo_data;
struct device_node *np = adap->dev.of_node;
muxc->adapter[muxc->num_adapters] = NULL;
snprintf(symlink_name, sizeof(symlink_name),
"channel-%u", priv->chan_id);
sysfs_remove_link(&muxc->dev->kobj, symlink_name);
sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
i2c_del_adapter(adap);
of_node_put(np);
kfree(priv);
}
}
EXPORT_SYMBOL_GPL(i2c_mux_del_adapters);
MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
MODULE_DESCRIPTION("I2C driver for multiplexed I2C busses");
MODULE_LICENSE("GPL v2");