Fix System hangs on black screen when reboot

[koba]

[Impact]
System hangs on black screen when reboot

[Fix]
Looks like our VBIOS/GOP generally fail to turn the DP dual mode adater
TMDS output buffers back on after a reboot. This leads to a black screen
after reboot if we turned the TMDS output buffers off prior to reboot.
And if i915 decides to do a fastboot the black screen will persist even
after i915 takes over.

Apparently this has been a problem ever since commit b2ccb822d376 ("drm/i915:Enable/disable TMDS output buffers in DP++ adaptor as needed") if one rebooted while the display was turned off. And things became worse with commit fe0f1e3bfdfe ("drm/i915: Shut down displays gracefully on reboot") since now we always turn the display off before a reboot.

This was reported on a RKL, but I confirmed the same behaviour on my
SNB as well. So looks pretty universal.

Let's fix this by explicitly turning the TMDS output buffers back on
in the encoder->shutdown() hook. Note that this gets called after irqs
have been disabled, so the i2c communication with the DP dual mode
adapter has to be performed via polling (which the gmbus code is
perfectly happy to do for us).

We also need a bit of care in handling DDI encoders which may or may
not be set up for HDMI output. Specifically ddc_pin will not be
populated for a DP only DDI encoder, in which case we don't want to
call intel_gmbus_get_adapter(). We can handle that by simply doing
the dual mode adapter type check before calling
intel_gmbus_get_adapter().
Ref: https://patchwork.freedesktop.org/series/96433/

[Test]
1. install kernel
2. reboot
3. check the monitor works well.

[Regression Potential]
Medium, patch has sent to patchwork but may have a upgraded version in the furtue.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-oem-5.14 - 5.14.0-1007.7

---------------
linux-oem-5.14 (5.14.0-1007.7) focal; urgency=medium

  * focal/linux-oem-5.14: 5.14.0-1007.7 -proposed tracker (LP: #1949349)

  * Intel I225-IT ethernet controller: igc: probe of 0000:02:00.0 failed with
    error -1 (LP: #1945576)
    - igc: Remove _I_PHY_ID checking
    - igc: Remove phy->type checking

  * Fix Screen freeze after resume from suspend with iGPU [1002:6987]
    (LP: #1949050)
    - drm/amdgpu: reenable BACO support for 699F:C7 polaris12 SKU
    - drm/amdgpu: add missing cleanups for Polaris12 UVD/VCE on suspend
    - drm/amdgpu: Fix crash on device remove/driver unload

  * Fail to detect audio output from external monitor (LP: #1948767)
    - ALSA: hda: intel: Allow repeatedly probing on codec configuration errors

  * Fix System hangs on black screen when reboot (LP: #1949321)
    - SAUCE: drm/i915: Don't request GMBUS to generate irqs when called while irqs
      are off
    - SAUCE: drm/i915/hdmi: Turn DP++ TMDS output buffers back on in
      encoder->shutdown()

 -- Timo Aaltonen <email address hidden> Mon, 01 Nov 2021 12:38:15 +0200

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 5.15.0-17.17

---------------
linux (5.15.0-17.17) jammy; urgency=medium

  * jammy/linux: 5.15.0-17.17 -proposed tracker (LP: #1957809)

 -- Andrea Righi <email address hidden> Thu, 13 Jan 2022 17:11:21 +0100

[Brian Murray (brian-murray)]

Ubuntu 21.10 (Impish Indri) has reached end of life, so this bug will not be fixed for that specific release.