[Bug 103159] [CI] igt at kms_plane_scaling - Test assertion failure function igt_drm_plane_commit Failed assertion: ret == 0

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103159

--- Comment #8 from krisman at collabora.co.uk ---
Regarding the pixel clock scaling exceeded issue: 

> > > [drm:skl_check_pipe_max_pixel_rate [i915]] Max supported pixel clock with
> > > scaling exceeded

The problem started to show after the following commit, which included a
verification during .atomic_check() to ensure the bandwidth for pixel flow is
enough for scaling operations.

73b0ca8ec76 ("drm/i915/skl+: consider max supported plane pixel rate while
scaling")

The verification always succeeds when upscaling, since that operation won't
increase the pixel rate, but it causes the same test to fail a while later,
when trying downscaling.

As far as I can tell, there is no issue with the verification algorithm
introduced by that commit, since it correctly calculates the desired pixel
rate.  The problem happens a little before that on the driver, when calculating
the required clock, because it doesn't take in consideration the scaling
property.  This is where I'm patching a fix.

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