feat: Add Release Specific LPM workarounds for AM62L

Add workarounds for AM62L LPM

Signed-off-by: Dhruva Gole <[email protected]>

Author: DhruvaG2000

source/devices/AM62LX/linux/Release_Specific.rst

@@ -9,3 +9,4 @@ Release Specific
    Release_Specific_Yocto_layer_Configuration
    Release_Specific_Migration_Guide
    Release_Specific_Kernel_Performance_Guide
+   Release_Specific_Workarounds

source/devices/AM62LX/linux/Release_Specific_Workarounds.rst

@@ -0,0 +1,74 @@
+###############################
+System Suspend Mode Workarounds
+###############################
+
+ARM Trusted Firmware side changes
+*********************************
+
+This patch updates the system suspend mode for the AM62L platform. After making the following changes, one
+needs to re-build the ARM Trusted Firmware and then re-package it in the :file:`tispl.bin` file to ensure
+the changes take effect. To learn more about TF-A and how to rebuild it, please refer to :ref:`_foundational-components-atf`.
+For rebuilding u-boot and generating the new :file:`tispl.bin` follow :ref:`Build-U-Boot-label`.
+
+.. code-block:: diff
+
+   diff --git a/plat/ti/k3/common/am62l_psci.c b/plat/ti/k3/common/am62l_psci.c
+   index 70f2aecdd..115729f4a 100644
+   --- a/plat/ti/k3/common/am62l_psci.c
+   +++ b/plat/ti/k3/common/am62l_psci.c
+   @@ -133,7 +133,7 @@ static void am62l_pwr_domain_suspend(const psci_power_state_t *target_state)
+   	/* TODO: Pass the mode passed from kernel using s2idle
+   	 * For now make mode=6 for RTC only + DDR and mdoe=0 for deepsleep
+   	 */
+   -       uint32_t mode = 0;
+   +       uint32_t mode = 6;
+
+   	core = plat_my_core_pos();
+   	proc_id = PLAT_PROC_START_ID + core;
+
+The change is made in :file:`plat/ti/k3/common/am62l_psci.c`, which is the new PSCI driver for AM62L in Arm Trusted Firmware.
+The :func:`am62l_pwr_domain_suspend` function has been modified to change the default system suspend mode from Deep Sleep
+to RTC only + DDR.
+
+The default mode indicates a deep sleep state, which provides the lowest latency wake-up but also consumes
+more power. In contrast, the new default mode, RTC only + DDR, offers a lower power consumption profile but at the cost
+of higher wake-up latency.
+
+This change sets the default system suspend mode indication to 6, which corresponds to the RTC only + DDR mode.
+
+This change is a temporary solution. A more robust solution is under development to pass a suspend parameter from the kernel
+by leveraging the s2idle mechanism.
+
+Linux-side changes
+******************
+
+Since there are a few new drivers in AM62L, they are yet to add suspend/resume support
+functionality in Linux. Hence, to avoid any blockers during suspend/resume of Linux
+make use of the :file:`k3-am62l3-evm-lpmdemo.dtb` instead of the regular :file:`k3-am62l3-evm.dtb`.
+
+One can find the DT source of this file from
+`here <https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-am62l3-evm-lpmdemo.dts?h=11.00.05>`__.
+
+The build instructions for generating a DTB from DTS can be found here: :ref:`kernel_users_guide_compiling_the_device_tree_binaries`
+
+The :file:`k3-am62l3-evm-lpmdemo.dtb` file disables many drivers which may not behave well during suspend/resume
+of the device. These are planned to be enabled in the future after fixing any suspend/resume related issues
+and thorough testing.
+
+How-to suspend/resume
+*********************
+
+To suspend the device, use the following command in Linux:
+
+.. code-block:: console
+
+   $ echo mem > /sys/power/state
+
+To resume the device, press the following button on the EVM:
+
+.. image:: /images/am62l_lpm_wakeup_evm_pin.jpg
+
+.. important::
+
+    Only the above button i.e. the RTC ext pin is wake up capable as of now. More wakeup sources
+    will be added in future Linux SDK releases.