drm/i915: Disable FBC across page-flipping
Page-flipping updates the scanout address, nukes the FBC compressed image and so forces an FBC update so that the displayed image remains consistent. However, page-flipping does not update the FBC registers themselves, which remain pointing to both the old address and the old CPU fence. Future updates to the new front-buffer (scanout) are then undetected! This first approach to demonstrate the issue and highlight the fix, simply disables FBC upon page-flip (a recompression will be forced on every flip so FBC becomes immaterial) and then re-enables FBC in the page-flip finish work function, so that the FBC registers are now pointing to the new framebuffer and front-buffer rendering works once more. Ideally, we want to only re-enable FBC after page-flipping is complete, as otherwise we are just wasting cycles and power (with needless recompression) whilst the page-flipping application is still running. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=33487Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Keith Packard <keithp@keithp.com>
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