doc: cmd: add documentation for scmi

This is a help text for scmi command.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Etienne Carriere <etienne.carriere@foss.st.com>

2 files changed, 127 insertions, 0 deletions

diff --git a/doc/usage/cmd/scmi.rst b/doc/usage/cmd/scmi.rst
new file mode 100644
index 0000000..9ea7e0e
--- /dev/null
+++ b/doc/usage/cmd/scmi.rst
@@ -0,0 +1,126 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+scmi command
+============
+
+Synopsis
+--------
+
+::
+
+    scmi info
+    scmi perm_dev <agent id> <device id> <flags>
+    scmi perm_proto <agent id> <device id> <protocol id> <flags>
+    scmi reset <agent id> <flags>
+
+Description
+-----------
+
+Arm System Control and Management Interface (SCMI hereafter) is a set of
+standardised interfaces to manage system resources, like clocks, power
+domains, pin controls, reset and so on, in a system-wide manner.
+
+An entity which provides those services is called a SCMI firmware (or
+SCMI server if you like) may be placed/implemented by EL3 software or
+by a dedicated system control processor (SCP) or else.
+
+A user of SCMI interfaces, including U-Boot, is called a SCMI agent and
+may issues commands, which are defined in each protocol for specific system
+resources, to SCMI server via a communication channel, called a transport.
+Those interfaces are independent from the server's implementation thanks to
+a transport layer.
+
+For more details, see the `SCMI specification`_.
+
+While most of system resources managed under SCMI protocols are implemented
+and handled as standard U-Boot devices, for example clk_scmi, scmi command
+provides additional management functionality against SCMI server.
+
+scmi info
+~~~~~~~~~
+    Show base information about SCMI server and supported protocols
+
+scmi perm_dev
+~~~~~~~~~~~~~
+    Allow or deny access permission to the device
+
+scmi perm_proto
+~~~~~~~~~~~~~~~
+    Allow or deny access to the protocol on the device
+
+scmi reset
+~~~~~~~~~~
+    Reset the already-configured permissions against the device
+
+Parameters are used as follows:
+
+<agent id>
+    SCMI Agent ID, hex value
+
+<device id>
+    SCMI Device ID, hex value
+
+    Please note that what a device means is not defined
+    in the specification.
+
+<protocol id>
+    SCMI Protocol ID, hex value
+
+    It must not be 0x10 (base protocol)
+
+<flags>
+    Flags to control the action, hex value
+
+    0 to deny, 1 to allow. The other values are reserved and allowed
+    values may depend on the implemented version of SCMI server in
+    the future. See SCMI specification for more details.
+
+Example
+-------
+
+Obtain basic information about SCMI server:
+
+::
+
+    => scmi info
+    SCMI device: scmi
+      protocol version: 0x20000
+      # of agents: 3
+          0: platform
+        > 1: OSPM
+          2: PSCI
+      # of protocols: 4
+          Power domain management
+          Performance domain management
+          Clock management
+          Sensor management
+      vendor: Linaro
+      sub vendor: PMWG
+      impl version: 0x20b0000
+
+Ask for access permission to device#0:
+
+::
+
+    => scmi perm_dev 1 0 1
+
+Reset configurations with all access permission settings retained:
+
+::
+
+    => scmi reset 1 0
+
+Configuration
+-------------
+
+The scmi command is only available if CONFIG_CMD_SCMI=y.
+Default n because this command is mainly for debug purpose.
+
+Return value
+------------
+
+The return value ($?) is set to 0 if the operation succeeded,
+1 if the operation failed or -1 if the operation failed due to
+a syntax error.
+
+.. _`SCMI specification`: https://developer.arm.com/documentation/den0056/e/?lang=en
diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index d8e23fc..1a626c0 100644
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -94,6 +94,7 @@ Shell commands
    cmd/rng
    cmd/saves
    cmd/sbi
+   cmd/scmi
    cmd/scp03
    cmd/seama
    cmd/setexpr