Anbernic RG353P and RG503 are both RK3566 based handheld gaming devices
from Anbernic.

Both devices have:
 - 2 SDMMC slots.
 - A Realtek rtl8821cs WiFi/Bluetooth adapter.
 - A mini HDMI port.
 - A USB C host port and a USB C otg port (currently only working as
   device).
 - Multiple GPIO buttons and a single ADC button.
 - Dual analog joysticks controlled via a GPIO mux.
 - A headphone jack with amplified stereo speakers via a SGM4865 amp.
 - A PWM based vibrator for force feedback.

The RG353P has:
 - 2GB LPDDR4 RAM.
 - A 32GB eMMC.
 - A 3.5 inch 640x480 4-lane DSI panel of unknown origin with an i2c
   controlled touchscreen (touchscreen is a Hynitron CST340).

The RG503 has:
 - 1GB LPDDR4 RAM.
 - A 5 inch 960x544 AMOLED 2-lane DSI/DBI panel manufactured by Samsung
   with part number ams495qa04. Data for this panel is provided via the
   DSI interface, however commands are sent via a 9-bit 3-wire SPI
   interface. The MISO pin of SPI3 of the SOC is wired to the input of
   the panel, so it must be bitbanged.

This devicetree enables the following hardware:
 - HDMI (plus audio).
 - Analog audio, including speakers.
 - All buttons.
 - All SDMMC/eMMC/SDIO controllers.
 - The ADC joysticks (note a pending patch is required to use them).
 - WiFi/Bluetooth (note out of tree drivers are required).
 - The PWM based vibrator motor.

The following hardware is not enabled:
 - The display panels (drivers are being written and there are issues
   with the upstream DSI and VOP2 subsystems).
 - Battery (driver pending).
 - Touchscreen on the RG353P (note the i2c2 bus is enabled for it).
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Link: https://lore.kernel.org/r/20220906210324.28986-4-macroalpha82@gmail.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>