[Bug 89002] [BSW] testdisplay shows black screen for HDMI 4K monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89002

--- Comment #2 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Jani Nikula from comment #1)
> [    4.836820] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU
> pipe C FIFO underrun
> 
> Ville, can we do 4k on bsw hdmi?

Not before we get the cdclk code fixed. These systems boot with cdclk @ 266MHz
which is too low. We need to increase it to 320MHz when driving 4k modes.
Patches are in some kind of review limbo, and there's another patch (reduce
cdclk guardband to 5% from 10%) I've not yet posted that is also needed for
HDMI 4k.

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