Re: [PATCH V8] drm/i915/skl: SKL CDCLK change on modeset tracking VCO

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On 03/10/2016 12:08 AM, Maarten Lankhorst wrote:
Op 09-03-16 om 22:58 schreef clinton.a.taylor@xxxxxxxxx:
From: Clint Taylor <clinton.a.taylor@xxxxxxxxx>

WARNING: Using ChromeOS with an eDP panel and a 4K@60 DP monitor connected
to DDI1 the system will hard hang during a cold boot. Occurs when DDI1
is enabled when the cdclk is less then required. DP connected to DDI2
and HPD on either port works correctly.

Set cdclk based on the max required pixel clock based on VCO
selected. Track boot vco instead of boot cdclk.

The vco is now tracked at the atomic level and all CRTCs updated if
the required vco is changed. Not tested with eDP v1.4 panels that
require 8640 vco due to availability.

V1: initial version
V2: add vco tracking in intel_dp_compute_config(), rename
skl_boot_cdclk.
V3: rebase, V2 feedback not possible as encoders are not aware of
atomic.
V4: track target vco is atomic state. modeset all CRTCs if vco changes
V5: rename atomic variable, cleaner if/else logic, use existing vco if
       encoder does not return a new vco value. check_patch.pl cleanup
V6: simplify logic in intel_modeset_checks.
V7: reorder an IF for readability and whitespace fix.
V8: use dev_cdclk for tracking new cdclk during atomic

Signed-off-by: Clint Taylor <clinton.a.taylor@xxxxxxxxx>

Is the hang in the commit message introduced by this commit, or fixed by this commit?

The hang is introduced by this commit. The hang isn't reproducible using Arch Linux this appears to be an existing issue that is exposed for the first time now that cdclk can change on SKL. This warning will only affect ChromeOS users using drm-intel-nightly as the backport to ChromeOS removes many of the atomic specific changes. It's also very strange that the issue only affects the encoder attached to DDI1 and its computation of dev_cdclk during a cold boot.



~Maarten


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