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4765d061d5
Moving the vrr push to happen before sampling the frame counter
was wrong. If we are already in vblank when the push is sent
the vblank exit will start immediately which causes the sampled
frame counter to correspond to the next frame instead of the current
frame.
So put things back into the original order (except we should
keep the vrr push within the irq disable section to avoid
pointless irq related delays here).
We'll just have to accept the tiny race that exists between
sampling the frame counter vs. vrr push. And let's at least
document said race properly in a comment.
I suppose we could try to minimize the race by sampling the frame
counter just before sending the push, but that would require
changing drm_crtc_arm_vblank_event() to accept a caller provided
vblank counter value, so leave it be for now. Another thing we
could do is change the vblank evasion to account for the case
where a push was already sent. That would anyway be required
for mailbox style updates. Currently mailbox updates are only
used by the legacy cursor, but we don't do a vrr push for those.
Cc: Manasi Navare <manasi.d.navare@intel.com>
Fixes: 6f9976bd13 ("drm/i915: Do vrr push before sampling the frame counter")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211117183103.27418-1-ville.syrjala@linux.intel.com
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.