[BUG - BISECTED] display not detected anymore

[Ville Syrjälä]

On Wed, Aug 18, 2021 at 01:20:54PM +0200, Heiko Carstens wrote:
> On Sat, Aug 14, 2021 at 02:46:27PM +0200, Heiko Carstens wrote:
> > Hello,
> > 
> > I have Fedora 33 running, and with the Fedore kernel update from 5.11
> > series to 5.12 my external monitor was not detected anymore. Same is
> > true with the Fedora supplied 5.13 kernel version.
> > 
> > So I tried with vanilla kernel 5.11 and latest git head from Linus'
> > tree. 5.11 works while latest git head does not. Bisecting the problem
> > points to commit 32c3d9b0f51e ("Merge tag 'drm-intel-next-2021-01-27'
> > of git://anongit.freedesktop.org/drm/drm-intel into drm-next").
> > 
> > Unfortunately it is a merge commit, so it looks like conflicting
> > changes have been made in the parent branches.
> > 
> > Hardware in use:
> > 
> > - ThinkPad X1 Yoga 4th / Carbon 7th
> > - Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz
> > 
> > The Thinkpad is connected to a ThinkPad Thunderbolt 3 Dock with a
> > Thunderbolt cable and a monitor (Eizo EV3285) is connected via
> > Displayport to the docking station.
> > 
> > The monitor is detected and works without any problems (4k at 60HZ)
> > before the above mentioned merge commit. With the commit and
> > afterwards it is not detected anymore and only the Thinkpad builtin
> > display can be used.
> > 
> > Any idea what went wrong? I can provide more information, or test
> > debug patches if wanted. Just let me know.
> 
> So looks like I made a mistake when bisecting (it literally took me
> two days due to the low power machine, even with a minimized kernel
> config). Anyway, looking into it again the first bad commit is
> 
> ef79d62b5ce5 ("drm/i915: Encapsulate dbuf state handling harder")
> 
> With that commit the display is not detected anymore, one commit
> before that it still works. So this one seems to be broken.
> 
> Ville, Stanislav, any idea how to fix this?
> 
> commit ef79d62b5ce53851901d6c1d21b74cbb9e27219b
> Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Date:   Fri Jan 22 22:56:32 2021 +0200
> 
>     drm/i915: Encapsulate dbuf state handling harder

That has nothing to do with display detection, so very mysterious.

Please file a bug at https://gitlab.freedesktop.org/drm/intel/issues/new
boot with drm.debug=0xe with both good and bad kernels and attach the
dmesg from both to the bug.

-- 
Ville Syrjälä
Intel