feat(pm_wakeup_sources): Add WKUP GPIO wakeup source for AM62L

When AM62L enters Deep Sleep, WKUP GPIO pins can wakeup the system if
they are configured. Detail how to configure the WKUP GPIO to wakeup the
system and give an example that is used in the device tree.

Signed-off-by: Kendall Willis <[email protected]>

Author: kwillis01

source/linux/Foundational_Components/Power_Management/pm_wakeup_sources.rst

@@ -58,6 +58,8 @@ valid for given low power modes:
    +==================================+============+================+
    | Real-Time Clock (RTC)            | Yes        | Yes            |
    +----------------------------------+------------+----------------+
+   | WKUP GPIO                        | Yes        | No             |
+   +----------------------------------+------------+----------------+
    | Main I/O Daisy Chain (Main UART) | Yes        | No             |
    +----------------------------------+------------+----------------+
    | USB Wakeup                       | Yes        | No             |
@@ -311,6 +313,8 @@ For example, to wakeup from Deep Sleep in 10 seconds, use the command like this:
 
       The system will enter the mode selected by DM on the basis on existing constraints.
 
+.. _pm_mcu_gpio_wakeup:
+
 ********
 MCU GPIO
 ********
@@ -399,6 +403,92 @@ MCU GPIO
    :ref:`LPM section<lpm_modes>`, wakeup from MCU_SPI0_D1 can be triggered
    by grounding Pin 4 on J8 MCU Header.
 
+*********
+WKUP GPIO
+*********
+
+.. ifconfig:: CONFIG_part_variant in ('AM62LX')
+
+   One of the most common ways to wakeup a system is by using some I/O activity.
+   I/O activity on the WKUP GPIOs can wakeup the system when the WKUP GPIO
+   controller is configured as a wakeup source. Refer to the ``wkup_gpio_key`` node
+   in
+   `k3-am62l3-evm-lpm-wkup-sources.dtso <https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-am62l3-evm-lpm-wkup-sources.dtso?h=11.02.08>`__
+   to use as a template to configure the desired WKUP GPIO as a wakeup capable
+   GPIO.
+
+   A brief guide to configuring an WKUP GPIO as wakeup:
+
+   1. Add "gpio-keys" as a compatible string, refer to
+      `gpio_keys kernel documentation <https://www.kernel.org/doc/Documentation/devicetree/bindings/input/gpio-keys.txt>`__
+      for details.
+
+      .. code-block:: dts
+
+         compatible = "gpio-keys";
+
+   2. Set the desired pinctrl.
+
+      .. code-block:: dts
+
+         pinctrl-names = "default";
+         pinctrl-0 = <&wake_wkupgpio0_pins_default>;
+
+   3. Setup the interrupt parent as WKUP GPIO, then setup the interrupt.
+
+      .. code-block:: dts
+
+         interrupt-parent = <&wkup_gpio0>;
+         interrupts = <0 IRQ_TYPE_EDGE_RISING>;
+
+   4. Create following child node as a ``switch`` node:
+
+      .. code-block:: dts
+
+         switch {
+                  label = "WKUPGPIO";
+                  linux,code = <143>;
+                  gpios = <&wkup_gpio0 0 GPIO_ACTIVE_LOW>;
+                  wakeup-source;
+         };
+
+      * label: Descriptive name of the switch node. If the WKUP GPIO node is setup
+        correctly, the label will appear under :file:`/proc/interrupts`.
+      * linux,code: Keycode to emit.
+      * gpios: the GPIO required to be used as the gpio-key.
+      * wakeup-source:
+        `wakeup-source <https://www.kernel.org/doc/Documentation/devicetree/bindings/power/wakeup-source.txt>`__
+        property describes devices which have wakeup capability.
+
+   5. To confirm that gpio_keys can wakeup the system from Deep Sleep, check
+      :file:`/proc/interrupts` for the label:
+
+      .. code-block:: console
+
+         root@<machine>:~# cat /proc/interrupts | grep "WKUPGPIO"
+         23:          0          0      GPIO   0 Edge    -davinci_gpio  WKUPGPIO
+
+   The WKUP GPIOs can be used to wakeup the system from Deep Sleep because WKUP
+   GPIOs are in a power domain that stays ON when the SoC is in Deep Sleep.
+   Hence, the GPIO controller is able to act as a wakeup source and send a
+   wakeup interrupt to the system.
+
+   WKUP GPIO wakeup can only be tested when
+   `k3-am62l3-evm-lpm-wkup-sources.dtso <https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-am62l3-evm-lpm-wkup-sources.dtso?h=11.02.08>`__
+   overlay is loaded. Refer to :ref:`How to enable DT overlays<howto_dt_overlays>` for more details.
+   The WKUP GPIO in the overlay is routed from the WKUP UART. With this
+   configuration the WKUP UART is not available as a wakeup source.
+
+   Once the system has entered Deep Sleep as shown in the
+   :ref:`LPM section<lpm_modes>`, wakeup from WKUP_UART0_RXD can be triggered
+   by entering a keypress on the WKUP UART (/dev/ttyUSB2).
+
+.. ifconfig:: CONFIG_part_variant in ('AM62X', 'AM62AX', 'AM62PX')
+
+   Setup of WKUP GPIO is the same process of MCU GPIO. Refer to the
+   :ref:`MCU GPIO section<pm_mcu_gpio_wakeup>` on how to configure wakeup from
+   WKUP GPIO.
+
 ********************
 Main I/O Daisy Chain
 ********************