ThinkPad X1 Extreme 2nd Generation does not advertise DPCD backlight in vbios

Submitted by Lyude Paul @lyudess

Assigned to Intel GFX Bugs mailing list

Link to original bug (#112376)

Description

Created attachment 146015
VBIOS

Filing this at the request of some of the Intel folks. I recently got my hand on a ThinkPad X1 Extreme 2nd Generation with the optional 4K AMOLED screen, and discovered that backlight controls weren't working. While there seems to be multiple problems here, all of which I've come up with some patches for that I plan to send out after filing this bug, one of the big things I noticed was that despite requiring DPCD backlight control this laptop claims to be using PWM backlight controls in it's vbios. So, I'm filing this bug to upload the vbios along with DPCD and other relevant information here.

As well, here's a dump of some relevant DPCD registers:

[ 3.142168] [drm:intel_dp_read_dpcd [i915]] DPCD: 14 14 c4 01 00 00 01 c0 02 14 00 00 00 08 82
[ 3.142600] [drm:drm_dp_read_desc [drm_kms_helper]] DP sink: OUI ba-41-59 dev-ID HW-rev 0.0 SW-rev 0.0 quirks 0x0000
[ 3.143012] [drm:intel_dp_init_connector [i915]] eDP DPCD: 05 9d a6

If you need any more information just let me know and I'll be happy to uplaod it

Attachment 146015, "VBIOS":
i915_vbt