[Intel-gfx] [PATCH] drm: i915: Preserve old FBC status for update without new planes

[Gabriel Krisman Bertazi]

Gabriel Krisman Bertazi <krisman at collabora.co.uk> writes:

> If the atomic commit doesn't include any new plane, there is no need to
> choose a new CRTC for FBC, and the intel_fbc_choose_crtc() will bail out
> early.  Although, if the FBC setup failed in the previous commit, if the
> current commit doesn't include new plane update, it tries to overwrite
> no_fbc_reason to "no suitable CRTC for FBC".  For that scenario, it is
> better that we simply keep the old message in-place to make debugging
> easier.
>
> A scenario where this happens is with the
> igt at kms_frontbuffer_tracking@fbc-suspend testcase when executed on a
> Haswell system with not enough stolen memory.  When enabling the CRTC,
> the FBC setup will be correctly initialized to a specific CRTC, but
> won't be enabled, since there is not enough memory.  The testcase will
> then enable CRC checking, which requires a quirk for Haswell, which
> issues a new atomic commit that doesn't update the planes.  Since that
> update doesn't include any new planes (and the FBC wasn't enabled),
> intel_fbc_choose_crtc() will not find any suitable CRTC, but update the
> error message, hiding the lack of memory information, which is the
> actual cause of the initialization failure.  As a result, this causes
> that test, which should skip, to fail on Haswell.
>
> Changes since v1:
>   - Update commit message (Manasi)
>

Hi Manasi,

(Resending this message, cause I think it bounced)

Unless there are other concerns about this one, can you help me get it
pushed? I don't have the commit rights.

Thanks!

-- 
Gabriel Krisman Bertazi