doc: usage: man-page for pinmux command

Provide a man-page for the pinmux command.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>

doc/usage/index.rst

@@ -36,6 +36,7 @@ Shell commands
    mbr
    md
    mmc
+   pinmux
    pstore
    qfw
    reset

doc/usage/pinmux.rst

@@ -0,0 +1,95 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+pinmux command
+==============
+
+Synopsis
+--------
+
+::
+
+    pinmux list
+    pinmux dev [pincontroller-name]
+    pinmux status [-a | pin-name]
+
+Description
+-----------
+
+The pinmux command is used to show the pin-controller muxing.
+
+The 'pinmux list' command diplays the available pin-controller.
+
+The 'pinmux dev' command selects the pin-controller for next commands.
+
+    pincontroller-name
+        name of the pin-controller to select
+
+The 'pinmux status' command displays the pin muxing information.
+
+    \-a
+        display pin muxing of all pin-controllers.
+    pin-name
+        name of the pin to display
+
+Example
+-------
+
+::
+
+    => pinmux list
+    | Device                        | Driver                        | Parent
+    | pinctrl-gpio                  | sandbox_pinctrl_gpio          | root_driver
+    | pinctrl                       | sandbox_pinctrl               | root_driver
+    =>
+    => pinmux dev pinctrl
+    dev: pinctrl
+    =>
+    => pinmux status
+    P0        : UART TX.
+    P1        : UART RX.
+    P2        : I2S SCK.
+    P3        : I2S SD.
+    P4        : I2S WS.
+    P5        : GPIO0 bias-pull-up input-disable.
+    P6        : GPIO1 drive-open-drain.
+    P7        : GPIO2 bias-pull-down input-enable.
+    P8        : GPIO3 bias-disable.
+    =>
+    => pinmux status P0
+    P0        : UART TX.
+    =>
+    => pinmux status -a
+    --------------------------
+    pinctrl-gpio:
+    a0        : gpio input .
+    a1        : gpio input .
+    a2        : gpio input .
+    a3        : gpio input .
+    a4        : gpio input .
+    a5        : gpio output .
+    a6        : gpio output .
+    a7        : gpio input .
+    a8        : gpio input .
+    a9        : gpio input .
+    --------------------------
+    pinctrl:
+    P0        : UART TX.
+    P1        : UART RX.
+    P2        : I2S SCK.
+    P3        : I2S SD.
+    P4        : I2S WS.
+    P5        : GPIO0 bias-pull-up input-disable.
+    P6        : GPIO1 drive-open-drain.
+    P7        : GPIO2 bias-pull-down input-enable.
+    P8        : GPIO3 bias-disable.
+
+Configuration
+-------------
+
+The pinmux command is only available if CONFIG_CMD_PINMUX=y.
+
+Return value
+------------
+
+The return value $? is set to 0 (true) if the command succeded and to 1 (false)
+otherwise.