linux/drivers/clk/clkdev.c
Sylwester Nawrocki 3a3d2b0551 clkdev: Fix race condition in clock lookup from device tree
There is currently a race condition in the device tree part of clk_get()
function, since the pointer returned from of_clk_get_by_name() may become
invalid before __clk_get() call. E.g. due to the clock provider driver
remove() callback being called in between of_clk_get_by_name() and
__clk_get().

Fix this by doing both the look up and __clk_get() operations with the
clock providers list mutex held. This ensures that the clock pointer
returned from __of_clk_get_from_provider() call and passed to __clk_get()
is valid, as long as the clock supplier module first removes its clock
provider instance and then does clk_unregister() on the corresponding
clocks.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
2013-12-04 17:19:36 +01:00

338 lines
7.5 KiB
C

/*
* drivers/clk/clkdev.c
*
* Copyright (C) 2008 Russell King.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Helper for the clk API to assist looking up a struct clk.
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/list.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/string.h>
#include <linux/mutex.h>
#include <linux/clk.h>
#include <linux/clkdev.h>
#include <linux/of.h>
#include "clk.h"
static LIST_HEAD(clocks);
static DEFINE_MUTEX(clocks_mutex);
#if defined(CONFIG_OF) && defined(CONFIG_COMMON_CLK)
struct clk *of_clk_get(struct device_node *np, int index)
{
struct of_phandle_args clkspec;
struct clk *clk;
int rc;
if (index < 0)
return ERR_PTR(-EINVAL);
rc = of_parse_phandle_with_args(np, "clocks", "#clock-cells", index,
&clkspec);
if (rc)
return ERR_PTR(rc);
of_clk_lock();
clk = __of_clk_get_from_provider(&clkspec);
if (!IS_ERR(clk) && !__clk_get(clk))
clk = ERR_PTR(-ENOENT);
of_clk_unlock();
of_node_put(clkspec.np);
return clk;
}
EXPORT_SYMBOL(of_clk_get);
/**
* of_clk_get_by_name() - Parse and lookup a clock referenced by a device node
* @np: pointer to clock consumer node
* @name: name of consumer's clock input, or NULL for the first clock reference
*
* This function parses the clocks and clock-names properties,
* and uses them to look up the struct clk from the registered list of clock
* providers.
*/
struct clk *of_clk_get_by_name(struct device_node *np, const char *name)
{
struct clk *clk = ERR_PTR(-ENOENT);
/* Walk up the tree of devices looking for a clock that matches */
while (np) {
int index = 0;
/*
* For named clocks, first look up the name in the
* "clock-names" property. If it cannot be found, then
* index will be an error code, and of_clk_get() will fail.
*/
if (name)
index = of_property_match_string(np, "clock-names", name);
clk = of_clk_get(np, index);
if (!IS_ERR(clk))
break;
else if (name && index >= 0) {
pr_err("ERROR: could not get clock %s:%s(%i)\n",
np->full_name, name ? name : "", index);
return clk;
}
/*
* No matching clock found on this node. If the parent node
* has a "clock-ranges" property, then we can try one of its
* clocks.
*/
np = np->parent;
if (np && !of_get_property(np, "clock-ranges", NULL))
break;
}
return clk;
}
EXPORT_SYMBOL(of_clk_get_by_name);
#endif
/*
* Find the correct struct clk for the device and connection ID.
* We do slightly fuzzy matching here:
* An entry with a NULL ID is assumed to be a wildcard.
* If an entry has a device ID, it must match
* If an entry has a connection ID, it must match
* Then we take the most specific entry - with the following
* order of precedence: dev+con > dev only > con only.
*/
static struct clk_lookup *clk_find(const char *dev_id, const char *con_id)
{
struct clk_lookup *p, *cl = NULL;
int match, best_found = 0, best_possible = 0;
if (dev_id)
best_possible += 2;
if (con_id)
best_possible += 1;
list_for_each_entry(p, &clocks, node) {
match = 0;
if (p->dev_id) {
if (!dev_id || strcmp(p->dev_id, dev_id))
continue;
match += 2;
}
if (p->con_id) {
if (!con_id || strcmp(p->con_id, con_id))
continue;
match += 1;
}
if (match > best_found) {
cl = p;
if (match != best_possible)
best_found = match;
else
break;
}
}
return cl;
}
struct clk *clk_get_sys(const char *dev_id, const char *con_id)
{
struct clk_lookup *cl;
mutex_lock(&clocks_mutex);
cl = clk_find(dev_id, con_id);
if (cl && !__clk_get(cl->clk))
cl = NULL;
mutex_unlock(&clocks_mutex);
return cl ? cl->clk : ERR_PTR(-ENOENT);
}
EXPORT_SYMBOL(clk_get_sys);
struct clk *clk_get(struct device *dev, const char *con_id)
{
const char *dev_id = dev ? dev_name(dev) : NULL;
struct clk *clk;
if (dev) {
clk = of_clk_get_by_name(dev->of_node, con_id);
if (!IS_ERR(clk))
return clk;
}
return clk_get_sys(dev_id, con_id);
}
EXPORT_SYMBOL(clk_get);
void clk_put(struct clk *clk)
{
__clk_put(clk);
}
EXPORT_SYMBOL(clk_put);
void clkdev_add(struct clk_lookup *cl)
{
mutex_lock(&clocks_mutex);
list_add_tail(&cl->node, &clocks);
mutex_unlock(&clocks_mutex);
}
EXPORT_SYMBOL(clkdev_add);
void __init clkdev_add_table(struct clk_lookup *cl, size_t num)
{
mutex_lock(&clocks_mutex);
while (num--) {
list_add_tail(&cl->node, &clocks);
cl++;
}
mutex_unlock(&clocks_mutex);
}
#define MAX_DEV_ID 20
#define MAX_CON_ID 16
struct clk_lookup_alloc {
struct clk_lookup cl;
char dev_id[MAX_DEV_ID];
char con_id[MAX_CON_ID];
};
static struct clk_lookup * __init_refok
vclkdev_alloc(struct clk *clk, const char *con_id, const char *dev_fmt,
va_list ap)
{
struct clk_lookup_alloc *cla;
cla = __clkdev_alloc(sizeof(*cla));
if (!cla)
return NULL;
cla->cl.clk = clk;
if (con_id) {
strlcpy(cla->con_id, con_id, sizeof(cla->con_id));
cla->cl.con_id = cla->con_id;
}
if (dev_fmt) {
vscnprintf(cla->dev_id, sizeof(cla->dev_id), dev_fmt, ap);
cla->cl.dev_id = cla->dev_id;
}
return &cla->cl;
}
struct clk_lookup * __init_refok
clkdev_alloc(struct clk *clk, const char *con_id, const char *dev_fmt, ...)
{
struct clk_lookup *cl;
va_list ap;
va_start(ap, dev_fmt);
cl = vclkdev_alloc(clk, con_id, dev_fmt, ap);
va_end(ap);
return cl;
}
EXPORT_SYMBOL(clkdev_alloc);
int clk_add_alias(const char *alias, const char *alias_dev_name, char *id,
struct device *dev)
{
struct clk *r = clk_get(dev, id);
struct clk_lookup *l;
if (IS_ERR(r))
return PTR_ERR(r);
l = clkdev_alloc(r, alias, alias_dev_name);
clk_put(r);
if (!l)
return -ENODEV;
clkdev_add(l);
return 0;
}
EXPORT_SYMBOL(clk_add_alias);
/*
* clkdev_drop - remove a clock dynamically allocated
*/
void clkdev_drop(struct clk_lookup *cl)
{
mutex_lock(&clocks_mutex);
list_del(&cl->node);
mutex_unlock(&clocks_mutex);
kfree(cl);
}
EXPORT_SYMBOL(clkdev_drop);
/**
* clk_register_clkdev - register one clock lookup for a struct clk
* @clk: struct clk to associate with all clk_lookups
* @con_id: connection ID string on device
* @dev_id: format string describing device name
*
* con_id or dev_id may be NULL as a wildcard, just as in the rest of
* clkdev.
*
* To make things easier for mass registration, we detect error clks
* from a previous clk_register() call, and return the error code for
* those. This is to permit this function to be called immediately
* after clk_register().
*/
int clk_register_clkdev(struct clk *clk, const char *con_id,
const char *dev_fmt, ...)
{
struct clk_lookup *cl;
va_list ap;
if (IS_ERR(clk))
return PTR_ERR(clk);
va_start(ap, dev_fmt);
cl = vclkdev_alloc(clk, con_id, dev_fmt, ap);
va_end(ap);
if (!cl)
return -ENOMEM;
clkdev_add(cl);
return 0;
}
/**
* clk_register_clkdevs - register a set of clk_lookup for a struct clk
* @clk: struct clk to associate with all clk_lookups
* @cl: array of clk_lookup structures with con_id and dev_id pre-initialized
* @num: number of clk_lookup structures to register
*
* To make things easier for mass registration, we detect error clks
* from a previous clk_register() call, and return the error code for
* those. This is to permit this function to be called immediately
* after clk_register().
*/
int clk_register_clkdevs(struct clk *clk, struct clk_lookup *cl, size_t num)
{
unsigned i;
if (IS_ERR(clk))
return PTR_ERR(clk);
for (i = 0; i < num; i++, cl++) {
cl->clk = clk;
clkdev_add(cl);
}
return 0;
}
EXPORT_SYMBOL(clk_register_clkdevs);