i915 intel_backlight turns off during boot on Google Pixel Slate (nocturne) due to improper AUX Backlight Control Support check.
Backlight is nonfunctional due to logic detecting AUX Backlight Control Support improperly.
Current solution (doubt acceptable for upstream) is available in comments below:
Debug info:
chronos@nocturne / $ sudo cat /sys/kernel/debug/dri/0/eDP-1/i915_dpcd
0000: 14 00 c4 41 00 00 01 80 02 00 00 00 0f 09 80
0070: 03 1b
0080: 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0100: 00 84 00 2a 2a 2a 2a 00 01 08 00
0200: 01 00 77 77 81 01 66 66
0600: 01
0700: 04
0701: fb ff 00 00
0720: 01 1a a4 70 10 0a 10 00 02 00 01 00 00 ff ff 03
0732: 00 14
sudo dd if=/dev/drm_dp_aux0 bs=1 skip=$((0x200)) count=1 2>/dev/null | xxd -p
01
sudo dd if=/dev/drm_dp_aux0 bs=1 skip=$((0x400)) count=12 2>/dev/null | xxd -p
001cf8000000000000010207
dmesg with kernel cmdline "drm.debug=0x1e log_buf_len=1M" attached:
5.7.10-050710-generic.dmesg.txt.gz 5.8.0-050800rc6drmtip20200722-generic.dmesg.txt.gz
edid: edid.gz
DPCD dump attempts via sudo ddrescue -O /dev/drm_dp_aux0
:
dpcd_aux0_ddrescue.gz dpcd_aux0_ddrescue2.gz dpcd_aux0_ddrescue_chromeos.gz dpcd_aux0_ddrescue_chromeos2.gz
fwts:
Edited by Satadru Pramanik