razer-cheryl2: Add device-specific notes

devices/razer-cheryl2/README.adoc

@@ -0,0 +1,36 @@
+= Razer Phone 2
+include::_support/common.inc[]
+
+== Device-specific notes
+
+=== Display problems
+
+The video drivers from the vendor do not support being used with the classic
+framebuffer.
+
+Only DRM (Direct Rendering Manager) is supported.
+
+A workaround, for the time being, is to use `simplefb`. Though when the device
+boots in the default system, the `simplefb` framebuffer stops working. It is
+suspected that it is the video drivers switching the display to HDR that are
+causing this issue.
+
+A workaround to help with this workaround has been implemented. When booted in
+the default system, the early init will reboot to recovery. In recovery mode
+the kernel does not exhibit this issue.
+
+The solution to this problem will be to properly support DRM-only workflows.
+
+Another avenue for solving this is to fix the fbdev emulation driver for the
+Qualcomm vendor tree.
+
+Yet another is to explore using mainline. Though it is unknown if the
+dual-DSI display, for which the vendor driver is unique, would work well with
+the generic code working with other SDM845 devices.
+
+=== Playing with the RGB logo
+
+```
+$ cd /sys/class/leds
+$ for f in *channel*/brightness *channel*/led_current; do echo 25 > $f; done
+```