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feat(pm_low_power_modes_socoff): Add LPM Documentation for J7200 and J784S4
J7200 and J784S4 supports two low poer modes, SOC_OFF and IO_ONLY_PLUS_DDR. Add related documentation for the modes supported and their usage details. Signed-off-by: Prasanth Babu Mantena <p-mantena@ti.com>
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‎configs/J7200/J7200_linux_toc.txt‎

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linux/Foundational_Components_Kernel_FAQs
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linux/Foundational_Components_Security
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linux/Foundational_Components/System_Security/Security_overview
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linux/Foundational_Components_Power_Management
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linux/Foundational_Components/Power_Management/pm_low_power_modes_socoff
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linux/Foundational_Components_Filesystem
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linux/Foundational_Components_Tools
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linux/Foundational_Components/Tools/Development_Tools

‎configs/J784S4/J784S4_linux_toc.txt‎

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linux/Foundational_Components_Kernel_FAQs
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linux/Foundational_Components_Security
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linux/Foundational_Components/System_Security/Security_overview
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linux/Foundational_Components_Power_Management
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linux/Foundational_Components/Power_Management/pm_low_power_modes_socoff
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linux/Foundational_Components_Filesystem
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linux/Foundational_Components_Tools
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linux/Foundational_Components/Tools/Development_Tools

‎source/linux/Foundational_Components/Power_Management/pm_low_power_modes_socoff.rst‎

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.. _lpm_modes_socoff:
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###############
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Low power modes
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###############
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********
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Overview
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********
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The following sections describe a high-level description of the different low power modes (LPM) supported on J7200 and J784S4 SOC.
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These modes are validated on TI EVMs. Selection of low power modes need to be done at build time, So user must decide, which low power mode meets the requirements.
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Each mode needs evaluation based on power consumption and latency (the time it takes to wake-up to Active mode) requirements.
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In SDK offering, following low power modes are supported:
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#. SOC OFF
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#. I/O Only Plus DDR
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*******
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SOC OFF
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*******
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In SOC OFF low-power mode, partial SW context (Mainly HLOS Linux) is retained in DDR while the SOC is turned off. This can save a significant amount of boot time, because it does not reinitialize whole kernel as it is already present in DDR.
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The benefits of using SOC OFF in embedded devices:
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#. Faster wake-up: devices can wake-up from this low-power state much faster than
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a complete power cycle.
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#. Better efficiency: This mode can help to improve the efficiency of embedded devices by
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reducing the amount of time that the processor is idle. This is because the processor can
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be kept in a low-power state when it is not needed.
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In order to enter SOC OFF, use the following command:
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.. code-block:: console
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root@<machine>-evm:~# echo mem > /sys/power/state
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[ 18.380346] PM: suspend entry (deep)
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[ 18.576999] Filesystems sync: 0.193 seconds
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[ 18.587643] Freezing user space processes
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[ 18.593191] Freezing user space processes completed (elapsed 0.001 seconds)
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[ 18.600179] OOM killer disabled.
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[ 18.603395] Freezing remaining freezable tasks
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[ 18.608964] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
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[ 18.616364] printk: Suspending console(s) (use no_console_suspend to debug)
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This indicates that linux has finished its suspend sequence.
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To exit from SOC OFF,
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.. ifconfig:: CONFIG_part_variant in ('J7200')
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Press SW12 push button on J7200 evm.
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.. ifconfig:: CONFIG_part_variant in ('J784S4')
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Press SW15 push button on J784S4 evm.
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*****************
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I/O Only Plus DDR
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*****************
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In I/O Only Plus DDR, only the I/O pins are active while the rest of the SoC is turned off.
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#. Low power consumption: IO Only mode can save a significant amount of power, especially in battery-powered
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devices. This is because the DDR is in self-refresh and except the IO pins, rest of the SOC is turned off.
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#. Better efficiency: I/O Only Plus DDR mode can help to improve the efficiency of embedded devices by reducing
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the amount of time that the processor is idle. This is because the processor can be kept in a low-power state when it is not needed.
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#. Respond to external wakeup sources: This allows the system to still respond to external events, while it is in a low-power state and wakeup faster improving boot time.
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.. ifconfig:: CONFIG_part_variant in ('J7200')
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To enter I/O only mode, Enable edge sensitive wakeup for MCAN1_RX pin by writing to PADCONFIG_11 (0x0011C02C)
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.. code-block:: console
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# devmem2 0x0011C02C w 0x20050000
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# echo mem > /sys/power/state
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.. ifconfig:: CONFIG_part_variant in ('J784S4')
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To enter I/O only mode, Enable level sensitive wakeup for MCU_MCAN0_RX pin by writing to WKUP_PADCONFIG_47 (at address 0x4301C0BC)
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.. code-block:: console
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# devmem2 0x4301C0BC w 0x20050180
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# echo mem > /sys/power/state
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.. code-block:: console
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root@<machine>-evm:~# echo mem > /sys/power/state
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[ 18.380346] PM: suspend entry (deep)
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[ 18.576999] Filesystems sync: 0.193 seconds
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[ 18.587643] Freezing user space processes
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[ 18.593191] Freezing user space processes completed (elapsed 0.001 seconds)
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[ 18.600179] OOM killer disabled.
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[ 18.603395] Freezing remaining freezable tasks
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[ 18.608964] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
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[ 18.616364] printk: Suspending console(s) (use no_console_suspend to debug)
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To exit from IO_ONLY_PLUS_DDR,
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.. ifconfig:: CONFIG_part_variant in ('J7200')
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Press SW1 push button on J7200 SOM
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.. ifconfig:: CONFIG_part_variant in ('J784S4')
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The second pin-out of J33 is MCU_MCAN0_RX [3] and it is directly connected to the SOC [2]
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3.3V should be applied on that pin to wake it up from low power.
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.. note::
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All low power mode supported implies all low power mode supported by the firmware as per firmware
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capabilities. `TISCI_MSG_QUERY_FW_CAPS <https://software-dl.ti.com/tisci/esd/latest/2_tisci_msgs/general/core.html#tisci-msg-query-fw-caps>`__
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can be sent to firmware to get the low power modes supported by firmware.

‎source/linux/Foundational_Components_Power_Management.rst‎

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Foundational_Components/Power_Management/pm_rtc_ddr
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Foundational_Components/Power_Management/pm_low_power_modes
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Foundational_Components/Power_Management/pm_am62lx_low_power_modes
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Foundational_Components/Power_Management/pm_low_power_modes_socoff
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Foundational_Components/Power_Management/pm_wakeup_sources
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Foundational_Components/Power_Management/pm_sw_arch
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Foundational_Components/Power_Management/pm_debug

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