[Bug 111179] [Regression]Multiple monitors via DP TB dock detection/resolution/layout failure after Skylake->Coffeelake upgrade

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111179

--- Comment #12 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Arcadiy Ivanov from comment #11)
> Thanks for looking at this.
> 
> Both Dell Precision 7510 (SKL) and Dell Precision 5540 (CFL) have the same
> TB capabilities, TB3 ***HBR2***. It's true, with HBR2 they don't support
> 2x4k at 60Hz(**), but the point of filing this bug was somewhat different -
> there was a change in behavior in monitor detection and resolution/refresh
> rate setting.
> 
> SKL was supporting 2x4k with auto-detection, which, given hardware
> limitations, means that it was settling on 2x4k at 30Hz mode all by itself.
> When an upgrade was made to CFL, this auto-detection stopped working
> properly - as you can see it tried to configure 2x4K at 60Hz and failed,
> without fallback to 2x4K at 30Hz.

Are you sure SKL used 30Hz? If it did then that was being done by some
userspace component. The kernel driver never does stuff like that (it just more
or less blindly tries to do what userspace asks).

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