4. Custom Kernel Journey - dmikey/retros GitHub Wiki

🧩 R36S Clone DTS Audit — EmuELEC 4.7 Compatibility

This document tracks the current status of DTS (Device Tree Source) hardware definitions for a clone R36S handheld running EmuELEC 4.7, based on a decompiled .dtb (rf3536k4ka.dtb) from the original device.

✅ Hardware Accounted For

Component	Status	Notes
SoC	✅ RK3326	Fully supported in upstream + EmuELEC kernel patches.
Display (LCD Panel)	✅ Present	`dsi@` node with `panel@` subtree; enables video output.
Backlight	✅ Present	Backlight node present (PWM or GPIO controlled).
Audio Codec / I2S	✅ Present	Audio system defined, likely via I2S to external codec.
Analog Sticks	✅ Present	ADC joystick or SARADC references included.
Power Management	✅ Present	Voltage regulators and power domains defined.
Battery / Fuel Gauge	✅ Present	Basic battery monitoring defined.
Storage (eMMC/SD)	✅ Present	MMC/SD card interface included.
USB Host	✅ Present	`usb@` or `dwc2` present, enables OTG/charging.
PWM Controller	✅ Present	Used for backlight brightness.
Thermal Zones / Cooling	✅ Present	CPU thermal sensors and passive cooling zones.
SPI & I2C Buses	✅ Present	Available for peripherals (PMIC, display, audio).
Framebuffer / DRM	✅ Present	Proper video pipeline appears defined.

🟡 Likely Present (But Unconfirmed)

Component	Status	Notes
GPIO Buttons (ABXY, D-pad, etc.)	🟡 Not defined in DTS	Likely hardcoded in vendor kernel source. Needs `gpio-keys` block.
Wi-Fi / Bluetooth	🟡 Probably not present	Typical R36S clones don’t include networking hardware.
Headphone Jack	🟡 Unclear	Audio works, but jack GPIO switch not defined.
Analog Trigger Support	🟡 Not defined	May require additional GPIO or ADC mapping.

❌ Missing or Not Declared

Component	Status	Notes
RTC (Real-Time Clock)	❌ Not found	No `rtc@` node. Timekeeping fallback likely uses fake-hwclock or NTP.
HDMI Output	❌ Not supported	RK3326 has no HDMI output.
Touchscreen	❌ Not applicable	No panel or driver support for touchscreen.
Camera (MIPI/ISP)	❌ Not applicable	Not relevant to this device class.

✅ Summary Table

Category	✅ Working	🟡 Unconfirmed	❌ Missing
Display	✅
Audio	✅	🟡 Headphone GPIO
Input	✅ Analog	🟡 GPIO buttons	❌ RTC
Power/Battery	✅
USB/Storage	✅
Networking		🟡 Possibly missing	❌ if needed
Timekeeping			❌ RTC

🔧 Action Items

Add gpio-keys block to map physical button inputs.
Probe GPIO pinout to match buttons to specific lines.
Optionally add rtc@ node if a real-time clock exists or emulate one.
Clean up DTS warnings (address formats, duplicate unit addresses, etc.).
Test backlight control and analog stick calibration under EmuELEC.