Commit bcabbcca authored by Ohad Ben-Cohen's avatar Ohad Ben-Cohen
Browse files

rpmsg: add virtio-based remote processor messaging bus



Add a virtio-based inter-processor communication bus, which enables
kernel drivers to communicate with entities, running on remote
processors, over shared memory using a simple messaging protocol.

Every pair of AMP processors share two vrings, which are used to send
and receive the messages over shared memory.

The header of every message sent on the rpmsg bus contains src and dst
addresses, which make it possible to multiplex several rpmsg channels on
the same vring.

Every rpmsg channel is a device on this bus. When a channel is added,
and an appropriate rpmsg driver is found and probed, it is also assigned
a local rpmsg address, which is then bound to the driver's callback.

When inbound messages carry the local address of a bound driver,
its callback is invoked by the bus.

This patch provides a kernel interface only; user space interfaces
will be later exposed by kernel users of this rpmsg bus.

Designed with Brian Swetland <swetland@google.com>.

Signed-off-by: default avatarOhad Ben-Cohen <ohad@wizery.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au> (virtio_ids.h)
Cc: Brian Swetland <swetland@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg KH <greg@kroah.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
parent 34ed5a33
What: /sys/bus/rpmsg/devices/.../name
Date: June 2011
KernelVersion: 3.3
Contact: Ohad Ben-Cohen <ohad@wizery.com>
Description:
Every rpmsg device is a communication channel with a remote
processor. Channels are identified with a (textual) name,
which is maximum 32 bytes long (defined as RPMSG_NAME_SIZE in
rpmsg.h).
This sysfs entry contains the name of this channel.
What: /sys/bus/rpmsg/devices/.../src
Date: June 2011
KernelVersion: 3.3
Contact: Ohad Ben-Cohen <ohad@wizery.com>
Description:
Every rpmsg device is a communication channel with a remote
processor. Channels have a local ("source") rpmsg address,
and remote ("destination") rpmsg address. When an entity
starts listening on one end of a channel, it assigns it with
a unique rpmsg address (a 32 bits integer). This way when
inbound messages arrive to this address, the rpmsg core
dispatches them to the listening entity (a kernel driver).
This sysfs entry contains the src (local) rpmsg address
of this channel. If it contains 0xffffffff, then an address
wasn't assigned (can happen if no driver exists for this
channel).
What: /sys/bus/rpmsg/devices/.../dst
Date: June 2011
KernelVersion: 3.3
Contact: Ohad Ben-Cohen <ohad@wizery.com>
Description:
Every rpmsg device is a communication channel with a remote
processor. Channels have a local ("source") rpmsg address,
and remote ("destination") rpmsg address. When an entity
starts listening on one end of a channel, it assigns it with
a unique rpmsg address (a 32 bits integer). This way when
inbound messages arrive to this address, the rpmsg core
dispatches them to the listening entity.
This sysfs entry contains the dst (remote) rpmsg address
of this channel. If it contains 0xffffffff, then an address
wasn't assigned (can happen if the kernel driver that
is attached to this channel is exposing a service to the
remote processor. This make it a local rpmsg server,
and it is listening for inbound messages that may be sent
from any remote rpmsg client; it is not bound to a single
remote entity).
What: /sys/bus/rpmsg/devices/.../announce
Date: June 2011
KernelVersion: 3.3
Contact: Ohad Ben-Cohen <ohad@wizery.com>
Description:
Every rpmsg device is a communication channel with a remote
processor. Channels are identified by a textual name (see
/sys/bus/rpmsg/devices/.../name above) and have a local
("source") rpmsg address, and remote ("destination") rpmsg
address.
A channel is first created when an entity, whether local
or remote, starts listening on it for messages (and is thus
called an rpmsg server).
When that happens, a "name service" announcement is sent
to the other processor, in order to let it know about the
creation of the channel (this way remote clients know they
can start sending messages).
This sysfs entry tells us whether the channel is a local
server channel that is announced (values are either
true or false).
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/).
1. 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).
2. 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_channel *rpdev,
void (*cb)(struct rpmsg_channel *, void *, int, void *, u32),
void *priv, u32 addr);
- 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.
3. 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 __devexit 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,
.drv.owner = THIS_MODULE,
.id_table = rpmsg_driver_sample_id_table,
.probe = rpmsg_sample_probe,
.callback = rpmsg_sample_cb,
.remove = __devexit_p(rpmsg_sample_remove),
};
static int __init init(void)
{
return register_rpmsg_driver(&rpmsg_sample_client);
}
module_init(init);
static void __exit fini(void)
{
unregister_rpmsg_driver(&rpmsg_sample_client);
}
module_exit(fini);
Note: a similar sample which can be built and loaded can be found
in samples/rpmsg/.
4. 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.
......@@ -134,6 +134,8 @@ source "drivers/iommu/Kconfig"
source "drivers/remoteproc/Kconfig"
source "drivers/rpmsg/Kconfig"
source "drivers/virt/Kconfig"
source "drivers/devfreq/Kconfig"
......
......@@ -127,6 +127,7 @@ obj-$(CONFIG_HWSPINLOCK) += hwspinlock/
obj-$(CONFIG_NFC) += nfc/
obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
obj-$(CONFIG_REMOTEPROC) += remoteproc/
obj-$(CONFIG_RPMSG) += rpmsg/
# Virtualization drivers
obj-$(CONFIG_VIRT_DRIVERS) += virt/
......
# RPMSG always gets selected by whoever wants it
config RPMSG
tristate
select VIRTIO
select VIRTIO_RING
obj-$(CONFIG_RPMSG) += virtio_rpmsg_bus.o
This diff is collapsed.
......@@ -414,6 +414,15 @@ struct hv_vmbus_device_id {
__attribute__((aligned(sizeof(kernel_ulong_t))));
};
/* rpmsg */
#define RPMSG_NAME_SIZE 32
#define RPMSG_DEVICE_MODALIAS_FMT "rpmsg:%s"
struct rpmsg_device_id {
char name[RPMSG_NAME_SIZE];
};
/* i2c */
#define I2C_NAME_SIZE 20
......
/*
* Remote processor messaging
*
* Copyright (C) 2011 Texas Instruments, Inc.
* Copyright (C) 2011 Google, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* * Neither the name Texas Instruments nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef _LINUX_RPMSG_H
#define _LINUX_RPMSG_H
#include <linux/types.h>
#include <linux/device.h>
#include <linux/mod_devicetable.h>
/* The feature bitmap for virtio rpmsg */
#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service notifications */
/**
* struct rpmsg_hdr - common header for all rpmsg messages
* @src: source address
* @dst: destination address
* @reserved: reserved for future use
* @len: length of payload (in bytes)
* @flags: message flags
* @data: @len bytes of message payload data
*
* Every message sent(/received) on the rpmsg bus begins with this header.
*/
struct rpmsg_hdr {
u32 src;
u32 dst;
u32 reserved;
u16 len;
u16 flags;
u8 data[0];
} __packed;
/**
* struct rpmsg_ns_msg - dynamic name service announcement message
* @name: name of remote service that is published
* @addr: address of remote service that is published
* @flags: indicates whether service is created or destroyed
*
* This message is sent across to publish a new service, or announce
* about its removal. When we receive these messages, an appropriate
* rpmsg channel (i.e device) is created/destroyed. In turn, the ->probe()
* or ->remove() handler of the appropriate rpmsg driver will be invoked
* (if/as-soon-as one is registered).
*/
struct rpmsg_ns_msg {
char name[RPMSG_NAME_SIZE];
u32 addr;
u32 flags;
} __packed;
/**
* enum rpmsg_ns_flags - dynamic name service announcement flags
*
* @RPMSG_NS_CREATE: a new remote service was just created
* @RPMSG_NS_DESTROY: a known remote service was just destroyed
*/
enum rpmsg_ns_flags {
RPMSG_NS_CREATE = 0,
RPMSG_NS_DESTROY = 1,
};
#define RPMSG_ADDR_ANY 0xFFFFFFFF
struct virtproc_info;
/**
* rpmsg_channel - devices that belong to the rpmsg bus are called channels
* @vrp: the remote processor this channel belongs to
* @dev: the device struct
* @id: device id (used to match between rpmsg drivers and devices)
* @src: local address
* @dst: destination address
* @ept: the rpmsg endpoint of this channel
* @announce: if set, rpmsg will announce the creation/removal of this channel
*/
struct rpmsg_channel {
struct virtproc_info *vrp;
struct device dev;
struct rpmsg_device_id id;
u32 src;
u32 dst;
struct rpmsg_endpoint *ept;
bool announce;
};
typedef void (*rpmsg_rx_cb_t)(struct rpmsg_channel *, void *, int, void *, u32);
/**
* struct rpmsg_endpoint - binds a local rpmsg address to its user
* @rpdev: rpmsg channel device
* @cb: rx callback handler
* @addr: local rpmsg address
* @priv: private data for the driver's use
*
* In essence, an rpmsg endpoint represents a listener on the rpmsg bus, as
* it binds an rpmsg address with an rx callback handler.
*
* Simple rpmsg drivers shouldn't use this struct directly, because
* things just work: every rpmsg driver provides an rx callback upon
* registering to the bus, and that callback is then bound to its rpmsg
* address when the driver is probed. When relevant inbound messages arrive
* (i.e. messages which their dst address equals to the src address of
* the rpmsg channel), the driver's handler is invoked to process it.
*
* More complicated drivers though, that do need to allocate additional rpmsg
* addresses, and bind them to different rx callbacks, must explicitly
* create additional endpoints by themselves (see rpmsg_create_ept()).
*/
struct rpmsg_endpoint {
struct rpmsg_channel *rpdev;
rpmsg_rx_cb_t cb;
u32 addr;
void *priv;
};
/**
* struct rpmsg_driver - rpmsg driver struct
* @drv: underlying device driver
* @id_table: rpmsg ids serviced by this driver
* @probe: invoked when a matching rpmsg channel (i.e. device) is found
* @remove: invoked when the rpmsg channel is removed
* @callback: invoked when an inbound message is received on the channel
*/
struct rpmsg_driver {
struct device_driver drv;
const struct rpmsg_device_id *id_table;
int (*probe)(struct rpmsg_channel *dev);
void (*remove)(struct rpmsg_channel *dev);
void (*callback)(struct rpmsg_channel *, void *, int, void *, u32);
};
int register_rpmsg_device(struct rpmsg_channel *dev);
void unregister_rpmsg_device(struct rpmsg_channel *dev);
int register_rpmsg_driver(struct rpmsg_driver *drv);
void unregister_rpmsg_driver(struct rpmsg_driver *drv);
void rpmsg_destroy_ept(struct rpmsg_endpoint *);
struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *,
rpmsg_rx_cb_t cb, void *priv, u32 addr);
int
rpmsg_send_offchannel_raw(struct rpmsg_channel *, u32, u32, void *, int, bool);
/**
* rpmsg_send() - send a message across to the remote processor
* @rpdev: the rpmsg channel
* @data: payload of message
* @len: length of payload
*
* This function sends @data of length @len on the @rpdev channel.
* The message will be sent to the remote processor which the @rpdev
* channel belongs to, using @rpdev's source and destination addresses.
* In case there are no TX buffers available, the function will block until
* one becomes available, or a timeout of 15 seconds elapses. When the latter
* happens, -ERESTARTSYS is returned.
*
* Can only be called from process context (for now).
*
* Returns 0 on success and an appropriate error value on failure.
*/
static inline int rpmsg_send(struct rpmsg_channel *rpdev, void *data, int len)
{
u32 src = rpdev->src, dst = rpdev->dst;
return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);
}
/**
* rpmsg_sendto() - send a message across to the remote processor, specify dst
* @rpdev: the rpmsg channel
* @data: payload of message
* @len: length of payload
* @dst: destination address
*
* This function sends @data of length @len to the remote @dst address.
* The message will be sent to the remote processor which the @rpdev
* channel belongs to, using @rpdev's source address.
* In case there are no TX buffers available, the function will block until
* one becomes available, or a timeout of 15 seconds elapses. When the latter
* happens, -ERESTARTSYS is returned.
*
* Can only be called from process context (for now).
*
* Returns 0 on success and an appropriate error value on failure.
*/
static inline
int rpmsg_sendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst)
{
u32 src = rpdev->src;
return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);