[Bug 105887] [GLK] no signal after switch resolution from 1080p at 23.98

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105887

--- Comment #65 from Clinton Taylor <clinton.a.taylor at intel.com> ---

> I can confirm that applying
> https://github.com/herrnst/ubuntu-bionic-kernel/commit/
> 3d664ae3c8831a51139efbb5298fc27a1bee4950 "i915/glk: effectively disable
> hdmi_12bps_possible()" does in fact solve the problem for me. It's my
> understanding this is a workaround rather than a proper fix. If I can supply
> logging, edid, or something that would be helpful towards a proper fix,
> please let me know.
> 

Thanks for the offer, however the failure doesn't actually show up in the logs.

This appears to be a transcoder disable sequencing issue. The driver sequence
has been confirmed as correct according to the Gemini Lake documentation. Why
this happens only at 12bpc is still a mystery.

A simple msleep(50); at the end of intel_ddi_disable_transcoder_func() appears
to resolve the issue. This is also a W/A and not the final solution.

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