[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

Lakshmi <lakshminarayana.vudum at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jani.nikula at intel.com
             Status|NEW                         |NEEDINFO

--- Comment #1 from Lakshmi <lakshminarayana.vudum at intel.com> ---
(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?

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