linux/Documentation/staging/rpmsg.rst
Linus Torvalds 617e7481d7 remoteproc updates for v5.9
This introduces a new "detached" state for remote processors that are
 deemed to be running at the time Linux boots and the infrastructure for
 "attaching" to these. It then introduces the support for performing this
 operation for the STM32 platform.
 
 The coredump functionality is moved out from the core file and gains
 support for an optional mode where the recovery phase awaits the
 notification from devcoredump that the dump should be released. This
 allows userspace to grab the coredump in scenarios where vmalloc space
 is too low for creating a complete copy of the coredump before handing
 this to devcoredump.
 
 A new character device based interface is introduced to allow tying the
 stoppage of a remote processor to the termination of a user space
 process. This is useful in situations when such process provides crucial
 resources/operations for the firmware running on the remote processor.
 
 The Texas Instrument K3 driver gains support for the C66x and C71x DSPs.
 
 Qualcomm remoteprocs gains support for stashing relocation information
 in IMEM, to aid post mortem debugging and the crash notification
 mechanism is generalized to be reusable in cases where loosely coupled
 drivers needs to know about the status of a remote processor. One such
 example is the IPA hardware block, which is jointly owned with the
 modem and migrated to this improved interface.
 
 It also introduces a number of bug fixes and debug improvements for the
 Qualcomm modem remoteproc driver.
 
 And it cleans up the inconsistent interface for remoteproc drivers to
 implement power management.
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Merge tag 'rproc-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/andersson/remoteproc

Pull remoteproc updates from Bjorn Andersson:
 "This introduces a new "detached" state for remote processors that are
  deemed to be running at the time Linux boots and the infrastructure
  for "attaching" to these. It then introduces the support for
  performing this operation for the STM32 platform.

  The coredump functionality is moved out from the core file and gains
  support for an optional mode where the recovery phase awaits the
  notification from devcoredump that the dump should be released. This
  allows userspace to grab the coredump in scenarios where vmalloc space
  is too low for creating a complete copy of the coredump before handing
  this to devcoredump.

  A new character device based interface is introduced to allow tying
  the stoppage of a remote processor to the termination of a user space
  process. This is useful in situations when such process provides
  crucial resources/operations for the firmware running on the remote
  processor.

  The Texas Instrument K3 driver gains support for the C66x and C71x
  DSPs.

  Qualcomm remoteprocs gains support for stashing relocation information
  in IMEM, to aid post mortem debugging and the crash notification
  mechanism is generalized to be reusable in cases where loosely coupled
  drivers needs to know about the status of a remote processor. One such
  example is the IPA hardware block, which is jointly owned with the
  modem and migrated to this improved interface.

  It also introduces a number of bug fixes and debug improvements for
  the Qualcomm modem remoteproc driver.

  And it cleans up the inconsistent interface for remoteproc drivers to
  implement power management"

* tag 'rproc-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/andersson/remoteproc: (56 commits)
  remoteproc: core: Register the character device interface
  remoteproc: Add remoteproc character device interface
  remoteproc: kill IPA notify code
  net: ipa: new notification infrastructure
  remoteproc: k3-dsp: Add support for C71x DSPs
  dt-bindings: remoteproc: k3-dsp: Update bindings for C71x DSPs
  remoteproc: k3-dsp: Add support for L2RAM loading on C66x DSPs
  remoteproc: k3-dsp: Add a remoteproc driver of K3 C66x DSPs
  dt-bindings: remoteproc: Add bindings for C66x DSPs on TI K3 SoCs
  remoteproc: k3: Add TI-SCI processor control helper functions
  remoteproc: Introduce rproc_of_parse_firmware() helper
  dt-bindings: arm: keystone: Add common TI SCI bindings
  remoteproc: qcom_q6v5_mss: Remove redundant running state
  remoteproc: qcom: q6v5: Update running state before requesting stop
  remoteproc: qcom_q6v5_mss: Add modem debug policy support
  remoteproc: qcom_q6v5_mss: Validate modem blob firmware size before load
  remoteproc: qcom_q6v5_mss: Validate MBA firmware size before load
  rpmsg: update documentation
  remoteproc: qcom_q6v5_mss: Add MBA log extraction support
  remoteproc: Add coredump debugfs entry
  ...
2020-08-11 11:17:45 -07:00

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ReStructuredText

============================================
Remote Processor Messaging (rpmsg) Framework
============================================
.. note::
This document describes the rpmsg bus and how to write rpmsg drivers.
To learn how to add rpmsg support for new platforms, check out remoteproc.txt
(also a resident of Documentation/).
Introduction
============
Modern SoCs typically employ heterogeneous remote processor devices in
asymmetric multiprocessing (AMP) configurations, which may be running
different instances of operating system, whether it's Linux or any other
flavor of real-time OS.
OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP.
Typically, the dual cortex-A9 is running Linux in a SMP configuration,
and each of the other three cores (two M3 cores and a DSP) is running
its own instance of RTOS in an AMP configuration.
Typically AMP remote processors employ dedicated DSP codecs and multimedia
hardware accelerators, and therefore are often used to offload CPU-intensive
multimedia tasks from the main application processor.
These remote processors could also be used to control latency-sensitive
sensors, drive random hardware blocks, or just perform background tasks
while the main CPU is idling.
Users of those remote processors can either be userland apps (e.g. multimedia
frameworks talking with remote OMX components) or kernel drivers (controlling
hardware accessible only by the remote processor, reserving kernel-controlled
resources on behalf of the remote processor, etc..).
Rpmsg is a virtio-based messaging bus that allows kernel drivers to communicate
with remote processors available on the system. In turn, drivers could then
expose appropriate user space interfaces, if needed.
When writing a driver that exposes rpmsg communication to userland, please
keep in mind that remote processors might have direct access to the
system's physical memory and other sensitive hardware resources (e.g. on
OMAP4, remote cores and hardware accelerators may have direct access to the
physical memory, gpio banks, dma controllers, i2c bus, gptimers, mailbox
devices, hwspinlocks, etc..). Moreover, those remote processors might be
running RTOS where every task can access the entire memory/devices exposed
to the processor. To minimize the risks of rogue (or buggy) userland code
exploiting remote bugs, and by that taking over the system, it is often
desired to limit userland to specific rpmsg channels (see definition below)
it can send messages on, and if possible, minimize how much control
it has over the content of the messages.
Every rpmsg device is a communication channel with a remote processor (thus
rpmsg devices are called channels). Channels are identified by a textual name
and have a local ("source") rpmsg address, and remote ("destination") rpmsg
address.
When a driver starts listening on a channel, its rx callback is bound with
a unique rpmsg local address (a 32-bit integer). This way when inbound messages
arrive, the rpmsg core dispatches them to the appropriate driver according
to their destination address (this is done by invoking the driver's rx handler
with the payload of the inbound message).
User API
========
::
int rpmsg_send(struct rpmsg_channel *rpdev, void *data, int len);
sends a message across to the remote processor on a given channel.
The caller should specify the channel, the data it wants to send,
and its length (in bytes). The message will be sent on the specified
channel, i.e. its source and destination address fields will be
set to the channel's src and dst addresses.
In case there are no TX buffers available, the function will block until
one becomes available (i.e. until the remote processor consumes
a tx buffer and puts it back on virtio's used descriptor ring),
or a timeout of 15 seconds elapses. When the latter happens,
-ERESTARTSYS is returned.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
int rpmsg_sendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst);
sends a message across to the remote processor on a given channel,
to a destination address provided by the caller.
The caller should specify the channel, the data it wants to send,
its length (in bytes), and an explicit destination address.
The message will then be sent to the remote processor to which the
channel belongs, using the channel's src address, and the user-provided
dst address (thus the channel's dst address will be ignored).
In case there are no TX buffers available, the function will block until
one becomes available (i.e. until the remote processor consumes
a tx buffer and puts it back on virtio's used descriptor ring),
or a timeout of 15 seconds elapses. When the latter happens,
-ERESTARTSYS is returned.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
int rpmsg_send_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
void *data, int len);
sends a message across to the remote processor, using the src and dst
addresses provided by the user.
The caller should specify the channel, the data it wants to send,
its length (in bytes), and explicit source and destination addresses.
The message will then be sent to the remote processor to which the
channel belongs, but the channel's src and dst addresses will be
ignored (and the user-provided addresses will be used instead).
In case there are no TX buffers available, the function will block until
one becomes available (i.e. until the remote processor consumes
a tx buffer and puts it back on virtio's used descriptor ring),
or a timeout of 15 seconds elapses. When the latter happens,
-ERESTARTSYS is returned.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
int rpmsg_trysend(struct rpmsg_channel *rpdev, void *data, int len);
sends a message across to the remote processor on a given channel.
The caller should specify the channel, the data it wants to send,
and its length (in bytes). The message will be sent on the specified
channel, i.e. its source and destination address fields will be
set to the channel's src and dst addresses.
In case there are no TX buffers available, the function will immediately
return -ENOMEM without waiting until one becomes available.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
int rpmsg_trysendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst)
sends a message across to the remote processor on a given channel,
to a destination address provided by the user.
The user should specify the channel, the data it wants to send,
its length (in bytes), and an explicit destination address.
The message will then be sent to the remote processor to which the
channel belongs, using the channel's src address, and the user-provided
dst address (thus the channel's dst address will be ignored).
In case there are no TX buffers available, the function will immediately
return -ENOMEM without waiting until one becomes available.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
int rpmsg_trysend_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
void *data, int len);
sends a message across to the remote processor, using source and
destination addresses provided by the user.
The user should specify the channel, the data it wants to send,
its length (in bytes), and explicit source and destination addresses.
The message will then be sent to the remote processor to which the
channel belongs, but the channel's src and dst addresses will be
ignored (and the user-provided addresses will be used instead).
In case there are no TX buffers available, the function will immediately
return -ENOMEM without waiting until one becomes available.
The function can only be called from a process context (for now).
Returns 0 on success and an appropriate error value on failure.
::
struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_device *rpdev,
rpmsg_rx_cb_t cb, void *priv,
struct rpmsg_channel_info chinfo);
every rpmsg address in the system is bound to an rx callback (so when
inbound messages arrive, they are dispatched by the rpmsg bus using the
appropriate callback handler) by means of an rpmsg_endpoint struct.
This function allows drivers to create such an endpoint, and by that,
bind a callback, and possibly some private data too, to an rpmsg address
(either one that is known in advance, or one that will be dynamically
assigned for them).
Simple rpmsg drivers need not call rpmsg_create_ept, because an endpoint
is already created for them when they are probed by the rpmsg bus
(using the rx callback they provide when they registered to the rpmsg bus).
So things should just work for simple drivers: they already have an
endpoint, their rx callback is bound to their rpmsg address, and when
relevant inbound messages arrive (i.e. messages which their dst address
equals to the src address of their rpmsg channel), the driver's handler
is invoked to process it.
That said, more complicated drivers might do need to allocate
additional rpmsg addresses, and bind them to different rx callbacks.
To accomplish that, those drivers need to call this function.
Drivers should provide their channel (so the new endpoint would bind
to the same remote processor their channel belongs to), an rx callback
function, an optional private data (which is provided back when the
rx callback is invoked), and an address they want to bind with the
callback. If addr is RPMSG_ADDR_ANY, then rpmsg_create_ept will
dynamically assign them an available rpmsg address (drivers should have
a very good reason why not to always use RPMSG_ADDR_ANY here).
Returns a pointer to the endpoint on success, or NULL on error.
::
void rpmsg_destroy_ept(struct rpmsg_endpoint *ept);
destroys an existing rpmsg endpoint. user should provide a pointer
to an rpmsg endpoint that was previously created with rpmsg_create_ept().
::
int register_rpmsg_driver(struct rpmsg_driver *rpdrv);
registers an rpmsg driver with the rpmsg bus. user should provide
a pointer to an rpmsg_driver struct, which contains the driver's
->probe() and ->remove() functions, an rx callback, and an id_table
specifying the names of the channels this driver is interested to
be probed with.
::
void unregister_rpmsg_driver(struct rpmsg_driver *rpdrv);
unregisters an rpmsg driver from the rpmsg bus. user should provide
a pointer to a previously-registered rpmsg_driver struct.
Returns 0 on success, and an appropriate error value on failure.
Typical usage
=============
The following is a simple rpmsg driver, that sends an "hello!" message
on probe(), and whenever it receives an incoming message, it dumps its
content to the console.
::
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/rpmsg.h>
static void rpmsg_sample_cb(struct rpmsg_channel *rpdev, void *data, int len,
void *priv, u32 src)
{
print_hex_dump(KERN_INFO, "incoming message:", DUMP_PREFIX_NONE,
16, 1, data, len, true);
}
static int rpmsg_sample_probe(struct rpmsg_channel *rpdev)
{
int err;
dev_info(&rpdev->dev, "chnl: 0x%x -> 0x%x\n", rpdev->src, rpdev->dst);
/* send a message on our channel */
err = rpmsg_send(rpdev, "hello!", 6);
if (err) {
pr_err("rpmsg_send failed: %d\n", err);
return err;
}
return 0;
}
static void rpmsg_sample_remove(struct rpmsg_channel *rpdev)
{
dev_info(&rpdev->dev, "rpmsg sample client driver is removed\n");
}
static struct rpmsg_device_id rpmsg_driver_sample_id_table[] = {
{ .name = "rpmsg-client-sample" },
{ },
};
MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_sample_id_table);
static struct rpmsg_driver rpmsg_sample_client = {
.drv.name = KBUILD_MODNAME,
.id_table = rpmsg_driver_sample_id_table,
.probe = rpmsg_sample_probe,
.callback = rpmsg_sample_cb,
.remove = rpmsg_sample_remove,
};
module_rpmsg_driver(rpmsg_sample_client);
.. note::
a similar sample which can be built and loaded can be found
in samples/rpmsg/.
Allocations of rpmsg channels
=============================
At this point we only support dynamic allocations of rpmsg channels.
This is possible only with remote processors that have the VIRTIO_RPMSG_F_NS
virtio device feature set. This feature bit means that the remote
processor supports dynamic name service announcement messages.
When this feature is enabled, creation of rpmsg devices (i.e. channels)
is completely dynamic: the remote processor announces the existence of a
remote rpmsg service by sending a name service message (which contains
the name and rpmsg addr of the remote service, see struct rpmsg_ns_msg).
This message is then handled by the rpmsg bus, which in turn dynamically
creates and registers an rpmsg channel (which represents the remote service).
If/when a relevant rpmsg driver is registered, it will be immediately probed
by the bus, and can then start sending messages to the remote service.
The plan is also to add static creation of rpmsg channels via the virtio
config space, but it's not implemented yet.