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Since DC now uses CRTC_VERTICAL_INTERRUPT0 as VBLANK irq trigger
and vblank interrupts actually happen earliest at start of vblank,
instead of a bit before vblank, we no longer need some of the
fudging logic to deal with too early vblank irq handling (grep for
lb_vblank_lead_lines). This itself fixes a pageflip scheduling
bug in DC, caused by uninitialized use of lb_vblank_lead_lines,
with a wrong startup value of 0. Thanks to the new vblank irq
trigger this value of zero is now actually correct for DC :).
A new problem is that vblank irq's race against pflip irq's,
and as both can fire at first line of vblank, it is no longer
guaranteed that vblank irq handling (therefore -> drm_handle_vblank()
-> drm_update_vblank_count()) executes before pflip irq handling
for a given vblank interval when a pageflip completes. Therefore
the vblank count and timestamps emitted to user-space as part of
the pageflip completion event will be often stale and cause new
timestamping and swap scheduling errors in user-space.
This was observed with large frequency on R9 380 Tonga Pro.
Fix this by enforcing a vblank count+timestamp update right
before emitting the pageflip completion event from the pflip
irq handler. The logic in core drm_update_vblank_count() makes
sure that no redundant or conflicting updates happen, iow. the
call turns into a no-op if it wasn't needed for that vblank,
burning a few microseconds of cpu time though.
Successfully tested on AMD R9 380 "Tonga Pro" (VI/DCE 10)
with DC enabled on the current DC staging branch. Independent
measurement of pageflip completion timing with special hardware
measurement equipment now confirms correct pageflip timestamps
and counts in the pageflip completion events.
v2: Review comments by Michel, drop outdated paragraph
about problem already fixed in 2nd patch of the series.
Add acked/r-b by Harry and Michel.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Acked-by: Harry Wentland <harry.wentland@amd.com> (v1)
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Cc: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.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.