mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
synced 2025-01-17 22:05:08 +00:00
a87e55f89f
Previously I was under the impression that the scanline counter reads 0 when the pipe is off. Turns out that's not correct, and instead the scanline counter simply stops when the pipe stops, and it retains it's last value until the pipe starts up again, at which point the scanline counter jumps to vblank start. These jumps can cause the timestamp to jump backwards by one frame. Since we use the timestamps to guesstimage also the frame counter value on gen2, that would cause the frame counter to also jump backwards, which leads to a massice difference from the previous value. The end result is that flips/vblank events don't appear to complete as they're stuck waiting for the frame counter to catch up to that massive difference. Fix the problem properly by actually making sure the scanline counter has started to move before we assume that it's safe to enable vblank processing. v2: Less pointless duplication in the code (Chris) Cc: stable@vger.kernel.org Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Fixes: b7792d8b54cc ("drm/i915: Wait for pipe to start before sampling vblank timestamps on gen2") Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171129153732.3612-1-ville.syrjala@linux.intel.com (cherry picked from commit 8fedd64dabc86d0f31a0d1e152be3aa23c323553) Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.