diff options
Diffstat (limited to 'Documentation/rpmsg.txt')
| -rw-r--r-- | Documentation/rpmsg.txt | 293 |
1 files changed, 0 insertions, 293 deletions
diff --git a/Documentation/rpmsg.txt b/Documentation/rpmsg.txt deleted file mode 100644 index f7edc3aa1e92..000000000000 --- a/Documentation/rpmsg.txt +++ /dev/null @@ -1,293 +0,0 @@ -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 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 = 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. |