[Bug 112376] ThinkPad X1 Extreme 2nd Generation does not advertise DPCD backlight in vbios

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=112376

--- Comment #2 from Lyude Paul <lyude at redhat.com> ---
(In reply to Lakshmi from comment #1)
> (In reply to Lyude Paul from comment #0)
> > Created attachment 146015 [details]
> > 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
> 
> How old is the kernel? Can you attach the full dmesg with kernel parameters
> drm.debug=0x1e log_buf_len=4M to see more information about the issue?

I'm seeing this with drm-tip, and I just rechecked today and the issue is still
present.
I'm about to attach the dmesg you asked for as well

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