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Daniel Vetter 7355965da2 drm/vkms: Forward timer right after drm_crtc_handle_vblank 
In

commit def35e7c59
Author: Shayenne Moura <shayenneluzmoura@gmail.com>
Date:   Wed Jan 30 14:06:36 2019 -0200

    drm/vkms: Bugfix extra vblank frame

we fixed the vblank counter to give accurate results outside of
drm_crtc_handle_vblank, which fixed bugs around vblank timestamps
being off-by-one and causing the vblank counter to jump when it
shouldn't.

The trouble is that this completely broke crc generation. Shayenne and
Rodrigo tracked this down to the vblank timestamp going backwards in
time somehow. Which then resulted in an underflow in drm_vblank.c
code, which resulted in all kinds of things breaking really badly.

The reason for this is that once we've called drm_crtc_handle_vblank
and the hrtimer isn't forwarded yet, we're returning a vblank
timestamp in the past. This race is really hard to hit since it's
small, except when you enable crc generation: In that case there's a
call to drm_crtc_accurate_vblank right in-betwen, so we're guaranteed
to hit the bug.

The fix is to roll the hrtimer forward _before_ we do the vblank
processing (which has a side-effect of incrementing the vblank
counter), and we always subtract one frame from the hrtimer - since
now it's always one frame in the future.

To make sure we don't hit this again also add a WARN_ON checking for
whether our timestamp is somehow moving into the past, which is never
should.

This also aligns more with how real hw works:
1. first all registers are updated with the new timestamp/vblank
counter values.
2. then an interrupt is generated
3. kernel interrupt handler eventually fires.

So doing this aligns vkms closer with what drm_vblank.c expects.
Document this also in a comment.

Cc: Shayenne Moura <shayenneluzmoura@gmail.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606084404.12014-1-daniel.vetter@ffwll.ch
2019-06-06 20:36:21 -03:00
arch The usual smattering of fixes and tunings that came in too late for the 2019-05-26 13:45:15 -07:00
block blk-mq: fix hang caused by freeze/unfreeze sequence 2019-05-23 10:25:26 -06:00
certs treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
crypto treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 102 2019-05-24 17:39:00 +02:00
Documentation dt-bindings: drm/bridge/synopsys: dw-hdmi: Add "unwedge" for ddc bus 2019-06-05 15:39:00 -04:00
drivers drm/vkms: Forward timer right after drm_crtc_handle_vblank 2019-06-06 20:36:21 -03:00
fs Bug fixes (including a regression fix) for ext4. 2019-05-25 15:03:12 -07:00
include drm/edid: Clean up DRM_EDID_DIGITAL_* flags 2019-06-06 16:05:03 +03:00
init treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
ipc treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 52 2019-05-24 17:36:42 +02:00
kernel Make the GCC 9 warning for sub struct memset go away. 2019-05-26 13:49:40 -07:00
lib for-linus-20190524 2019-05-24 16:02:14 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 98 2019-05-24 17:37:54 +02:00
net SPDX update for 5.2-rc2, round 2 2019-05-24 14:31:58 -07:00
samples treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
scripts Devicetree fixes for 5.2: 2019-05-24 15:16:46 -07:00
security SPDX update for 5.2-rc2, round 2 2019-05-24 14:31:58 -07:00
sound treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 119 2019-05-24 17:39:02 +02:00
tools The usual smattering of fixes and tunings that came in too late for the 2019-05-26 13:45:15 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt The usual smattering of fixes and tunings that came in too late for the 2019-05-26 13:45:15 -07:00
.clang-format Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-17 11:26:25 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes
.gitignore .gitignore: exclude .get_maintainer.ignore and .gitattributes 2019-05-18 11:49:54 +09:00
.mailmap A reasonably busy cycle for docs, including: 2019-05-08 12:42:50 -07:00
COPYING
CREDITS Char/Misc driver patches for 5.1-rc1 2019-03-06 14:18:59 -08:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge remote-tracking branch 'drm/drm-next' into drm-misc-next 2019-05-28 09:39:08 +02:00
Makefile Linux 5.2-rc2 2019-05-26 16:49:19 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.