rpmsg.txt: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - mark document and chapter titles; - mark notes; - mark literal blocks; - adjust identation. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Mauro Carvalho Chehab
Jonathan Corbet
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============================================
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Remote Processor Messaging (rpmsg) Framework
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============================================
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Note: this document describes the rpmsg bus and how to write rpmsg drivers.
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.. note::
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This document describes the rpmsg bus and how to write rpmsg drivers.
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To learn how to add rpmsg support for new platforms, check out remoteproc.txt
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(also a resident of Documentation/).
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1. Introduction
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Introduction
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============
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Modern SoCs typically employ heterogeneous remote processor devices in
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asymmetric multiprocessing (AMP) configurations, which may be running
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@ -58,10 +63,14 @@ to their destination address (this is done by invoking the driver's rx handler
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with the payload of the inbound message).
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2. User API
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User API
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========
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::
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int rpmsg_send(struct rpmsg_channel *rpdev, void *data, int len);
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- sends a message across to the remote processor on a given channel.
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sends a message across to the remote processor on a given channel.
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The caller should specify the channel, the data it wants to send,
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and its length (in bytes). The message will be sent on the specified
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channel, i.e. its source and destination address fields will be
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@ -72,14 +81,20 @@ with the payload of the inbound message).
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a tx buffer and puts it back on virtio's used descriptor ring),
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or a timeout of 15 seconds elapses. When the latter happens,
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-ERESTARTSYS is returned.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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int rpmsg_sendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst);
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- sends a message across to the remote processor on a given channel,
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sends a message across to the remote processor on a given channel,
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to a destination address provided by the caller.
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The caller should specify the channel, the data it wants to send,
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its length (in bytes), and an explicit destination address.
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The message will then be sent to the remote processor to which the
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channel belongs, using the channel's src address, and the user-provided
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dst address (thus the channel's dst address will be ignored).
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@ -89,13 +104,19 @@ with the payload of the inbound message).
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a tx buffer and puts it back on virtio's used descriptor ring),
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or a timeout of 15 seconds elapses. When the latter happens,
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-ERESTARTSYS is returned.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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int rpmsg_send_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
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void *data, int len);
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- sends a message across to the remote processor, using the src and dst
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sends a message across to the remote processor, using the src and dst
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addresses provided by the user.
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The caller should specify the channel, the data it wants to send,
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its length (in bytes), and explicit source and destination addresses.
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The message will then be sent to the remote processor to which the
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@ -107,11 +128,15 @@ with the payload of the inbound message).
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a tx buffer and puts it back on virtio's used descriptor ring),
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or a timeout of 15 seconds elapses. When the latter happens,
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-ERESTARTSYS is returned.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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int rpmsg_trysend(struct rpmsg_channel *rpdev, void *data, int len);
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- sends a message across to the remote processor on a given channel.
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sends a message across to the remote processor on a given channel.
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The caller should specify the channel, the data it wants to send,
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and its length (in bytes). The message will be sent on the specified
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channel, i.e. its source and destination address fields will be
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@ -119,27 +144,40 @@ with the payload of the inbound message).
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In case there are no TX buffers available, the function will immediately
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return -ENOMEM without waiting until one becomes available.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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int rpmsg_trysendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst)
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- sends a message across to the remote processor on a given channel,
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sends a message across to the remote processor on a given channel,
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to a destination address provided by the user.
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The user should specify the channel, the data it wants to send,
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its length (in bytes), and an explicit destination address.
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The message will then be sent to the remote processor to which the
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channel belongs, using the channel's src address, and the user-provided
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dst address (thus the channel's dst address will be ignored).
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In case there are no TX buffers available, the function will immediately
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return -ENOMEM without waiting until one becomes available.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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int rpmsg_trysend_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
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void *data, int len);
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- sends a message across to the remote processor, using source and
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sends a message across to the remote processor, using source and
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destination addresses provided by the user.
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The user should specify the channel, the data it wants to send,
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its length (in bytes), and explicit source and destination addresses.
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The message will then be sent to the remote processor to which the
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@ -148,13 +186,17 @@ with the payload of the inbound message).
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In case there are no TX buffers available, the function will immediately
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return -ENOMEM without waiting until one becomes available.
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The function can only be called from a process context (for now).
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Returns 0 on success and an appropriate error value on failure.
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::
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struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *rpdev,
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void (*cb)(struct rpmsg_channel *, void *, int, void *, u32),
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void *priv, u32 addr);
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- every rpmsg address in the system is bound to an rx callback (so when
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every rpmsg address in the system is bound to an rx callback (so when
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inbound messages arrive, they are dispatched by the rpmsg bus using the
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appropriate callback handler) by means of an rpmsg_endpoint struct.
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@ -186,29 +228,44 @@ with the payload of the inbound message).
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Returns a pointer to the endpoint on success, or NULL on error.
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::
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void rpmsg_destroy_ept(struct rpmsg_endpoint *ept);
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- destroys an existing rpmsg endpoint. user should provide a pointer
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destroys an existing rpmsg endpoint. user should provide a pointer
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to an rpmsg endpoint that was previously created with rpmsg_create_ept().
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::
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int register_rpmsg_driver(struct rpmsg_driver *rpdrv);
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- registers an rpmsg driver with the rpmsg bus. user should provide
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registers an rpmsg driver with the rpmsg bus. user should provide
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a pointer to an rpmsg_driver struct, which contains the driver's
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->probe() and ->remove() functions, an rx callback, and an id_table
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specifying the names of the channels this driver is interested to
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be probed with.
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::
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void unregister_rpmsg_driver(struct rpmsg_driver *rpdrv);
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- unregisters an rpmsg driver from the rpmsg bus. user should provide
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unregisters an rpmsg driver from the rpmsg bus. user should provide
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a pointer to a previously-registered rpmsg_driver struct.
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Returns 0 on success, and an appropriate error value on failure.
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3. Typical usage
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Typical usage
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=============
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The following is a simple rpmsg driver, that sends an "hello!" message
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on probe(), and whenever it receives an incoming message, it dumps its
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content to the console.
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::
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/rpmsg.h>
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@ -256,10 +313,13 @@ static struct rpmsg_driver rpmsg_sample_client = {
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};
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module_rpmsg_driver(rpmsg_sample_client);
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Note: a similar sample which can be built and loaded can be found
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.. note::
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a similar sample which can be built and loaded can be found
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in samples/rpmsg/.
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4. Allocations of rpmsg channels:
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Allocations of rpmsg channels
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=============================
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At this point we only support dynamic allocations of rpmsg channels.
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