drivers: Introduce a simplified remoteproc framework

Many System on Chip(SoC) solutions are complex with multiple processors
on the same die dedicated to either general purpose of specialized
functions. Many examples do exist in today's SoCs from various vendors.
Typical examples are micro controllers such as an ARM M3/M0 doing a
offload of specific function such as event integration or power
management or controlling camera etc.

Traditionally, the responsibility of loading up such a processor with a
firmware and communication has been with a High Level Operating
System(HLOS) such as Linux. However, there exists classes of products
where Linux would need to expect services from such a processor or the
delay of Linux and operating system being able to load up such a
firmware is unacceptable.

To address these needs, we need some minimal capability to load such a
system and ensure it is started prior to an Operating System(Linux or
any other) is started up.

NOTE: This is NOT meant to be a solve-all solution, instead, it tries to
address certain class of SoCs and products that need such a solution.

A very simple model is introduced here as part of the initial support
that supports microcontrollers with internal memory (no MMU, no
execution from external memory, or specific image format needs). This
basic framework can then (hopefully) be extensible to other complex SoC
processor support as need be.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Simon Glass <sjg@chromium.org>

1 files changed, 168 insertions, 0 deletions

diff --git a/doc/driver-model/remoteproc-framework.txt b/doc/driver-model/remoteproc-framework.txt
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+#
+# (C) Copyright 2015
+# Texas Instruments Incorporated - http://www.ti.com/
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
+Remote Processor Framework
+==========================
+TOC:
+1. Introduction
+2. How does it work - The driver
+3. Describing the device using platform data
+4. Describing the device using device tree
+
+1. Introduction
+===============
+
+This is an introduction to driver-model for Remote Processors found
+on various System on Chip(SoCs). The term remote processor is used to
+indicate that this is not the processor on which U-Boot is operating
+on, instead is yet another processing entity that may be controlled by
+the processor on which we are functional.
+
+The simplified model depends on a single UCLASS - UCLASS_REMOTEPROC
+
+UCLASS_REMOTEPROC:
+- drivers/remoteproc/rproc-uclass.c
+- include/remoteproc.h
+
+Commands:
+- common/cmd_remoteproc.c
+
+Configuration:
+CONFIG_REMOTEPROC is selected by drivers as needed
+CONFIG_CMD_REMOTEPROC for the commands if required.
+
+2. How does it work - The driver
+=================================
+
+Overall, the driver statemachine transitions are typically as follows:
+        (entry)
+        +-------+
+    +---+ init  |
+    |   |       | <---------------------+
+    |   +-------+                       |
+    |                                   |
+    |                                   |
+    |   +--------+                      |
+Load|   |  reset |                      |
+    |   |        | <----------+         |
+    |   +--------+            |         |
+    |        |Load            |         |
+    |        |                |         |
+    |   +----v----+   reset   |         |
+    +-> |         |    (opt)  |         |
+        |  Loaded +-----------+         |
+        |         |                     |
+        +----+----+                     |
+             | Start                    |
+         +---v-----+        (opt)       |
+      +->| Running |        Stop        |
+Ping  +- |         +--------------------+
+(opt)    +---------+
+
+(is_running does not change state)
+opt: Optional state transition implemented by driver.
+
+NOTE: It depends on the remote processor as to the exact behavior
+of the statemachine, remoteproc core does not intent to implement
+statemachine logic. Certain processors may allow start/stop without
+reloading the image in the middle, certain other processors may only
+allow us to start the processor(image from a EEPROM/OTP) etc.
+
+It is hence the responsibility of the driver to handle the requisite
+state transitions of the device as necessary.
+
+Basic design assumptions:
+
+Remote processor can operate on a certain firmware that maybe loaded
+and released from reset.
+
+The driver follows a standard UCLASS DM.
+
+in the bare minimum form:
+
+static const struct dm_rproc_ops sandbox_testproc_ops = {
+	.load = sandbox_testproc_load,
+	.start = sandbox_testproc_start,
+};
+
+static const struct udevice_id sandbox_ids[] = {
+	{.compatible = "sandbox,test-processor"},
+	{}
+};
+
+U_BOOT_DRIVER(sandbox_testproc) = {
+	.name = "sandbox_test_proc",
+	.of_match = sandbox_ids,
+	.id = UCLASS_REMOTEPROC,
+	.ops = &sandbox_testproc_ops,
+	.probe = sandbox_testproc_probe,
+};
+
+This allows for the device to be probed as part of the "init" command
+or invocation of 'rproc_init()' function as the system dependencies define.
+
+The driver is expected to maintain it's own statemachine which is
+appropriate for the device it maintains. It must, at the very least
+provide a load and start function. We assume here that the device
+needs to be loaded and started, else, there is no real purpose of
+using the remoteproc framework.
+
+3. Describing the device using platform data
+============================================
+
+*IMPORTANT* NOTE: THIS SUPPORT IS NOT MEANT FOR USE WITH NEWER PLATFORM
+SUPPORT. THIS IS ONLY FOR LEGACY DEVICES. THIS MODE OF INITIALIZATION
+*WILL* BE EVENTUALLY REMOVED ONCE ALL NECESSARY PLATFORMS HAVE MOVED
+TO DM/FDT.
+
+Considering that many platforms are yet to move to device-tree model,
+a simplified definition of a device is as follows:
+
+struct dm_rproc_uclass_pdata proc_3_test = {
+	.name = "proc_3_legacy",
+	.mem_type = RPROC_INTERNAL_MEMORY_MAPPED,
+	.driver_plat_data = &mydriver_data;
+};
+
+U_BOOT_DEVICE(proc_3_demo) = {
+	.name = "sandbox_test_proc",
+	.platdata = &proc_3_test,
+};
+
+There can be additional data that may be desired depending on the
+remoteproc driver specific needs (for example: SoC integration
+details such as clock handle or something similar). See appropriate
+documentation for specific remoteproc driver for further details.
+These are passed via driver_plat_data.
+
+3. Describing the device using device tree
+==========================================
+/ {
+	...
+	aliases {
+		...
+		remoteproc0 = &rproc_1;
+		remoteproc1 = &rproc_2;
+
+	};
+	...
+
+	rproc_1: rproc@1 {
+		compatible = "sandbox,test-processor";
+		remoteproc-name = "remoteproc-test-dev1";
+	};
+
+	rproc_2: rproc@2 {
+		compatible = "sandbox,test-processor";
+		internal-memory-mapped;
+		remoteproc-name = "remoteproc-test-dev2";
+	};
+	...
+};
+
+aliases usage is optional, but it is usually recommended to ensure the
+users have a consistent usage model for a platform.
+the compatible string used here is specific to the remoteproc driver involved.