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Daniel Vetter 9d54fcd541 drm/gem-fb-helper: Always do implicit sync
I've done a lot of history digging. The first signs of this
optimization was introduced in i915:

commit 25067bfc06
Author: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Date:   Wed Sep 10 12:03:17 2014 -0300

    drm/i915: pin sprite fb only if it changed

without much justification. Pinning already pinned stuff is real cheap
(it's just obj->pin_count++ really), and the missing implicit sync was
entirely forgotten about it seems. It's at least not mentioned
anywhere it the commit message.

It was also promptly removed shortly afterwards in

commit ea2c67bb4a
Author: Matt Roper <matthew.d.roper@intel.com>
Date:   Tue Dec 23 10:41:52 2014 -0800

    drm/i915: Move to atomic plane helpers (v9)

again without really mentioning the side-effect that plane updates
with the same fb now again obey implicit syncing.

Note that this only ever applied to the plane_update hook, all other
legacy entry points (set_base, page_flip) always obeyed implicit sync
in the drm/i915 driver.

The real source of this code here seems to be msm, copied to vc4, then
copied to tinydrm. I've also tried to dig around in all available msm
sources, but the corresponding check for fb != old_fb is present ever
since the initial merge in

commit cf3a7e4ce0
Author: Rob Clark <robdclark@gmail.com>
Date:   Sat Nov 8 13:21:06 2014 -0500

    drm/msm: atomic core bits

The only older version I've found of msm atomic code predates the
atomic helpers, and so didn't even use any of this. It also does not
have a corresponding check (because it simply did no implicit sync at
all).

I've chatted with Rob on irc, and he didn't remember the reason for
this either.

Note we had epic amounts of fun with too much syncing against
_vblank_, especially around cursor updates. But I don't ever
discussing a need for less syncing against implicit fences.

Also note that explicit fencing allows you to sidetrack all of this,
at least for all the drivers correctly implemented using
drm_atomic_set_fence_for_plane().

Given that it seems to be an accident of history, and that big drivers
like i915 (and also nouveau it seems, I didn't follow the
amdgpu/radeon sync code to figure this out properly there) never have
done it, let's remove this.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405154449.23038-8-daniel.vetter@ffwll.ch
2018-06-20 14:43:13 +02:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-29 10:06:05 -07:00
block Revert "blk-mq: remove code for dealing with remapping queue" 2018-04-25 09:49:22 -06:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto crypto: drbg - set freed buffers to NULL 2018-04-21 00:57:00 +08:00
Documentation display: panel: Add AUO g070vvn01 display support (800x480) 2018-05-29 16:22:43 +02:00
drivers drm/gem-fb-helper: Always do implicit sync 2018-06-20 14:43:13 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Fix misc. bugs and a regression for ext4. 2018-04-28 20:07:21 -07:00
include drm: Add checks for atomic_[duplicate/destroy]_state with atomic drivers 2018-06-18 09:20:51 +02:00
init Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-15 16:12:35 -07:00
ipc ipc/shm: fix use-after-free of shm file via remap_file_pages() 2018-04-13 17:10:27 -07:00
kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-29 09:03:25 -07:00
lib Driver core fixes for 4.17-rc3 2018-04-27 10:12:20 -07:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
mm x86/pti: Filter at vma->vm_page_prot population 2018-04-25 11:02:51 +02:00
net A CephFS quota follow-up and fixes for two older issues in the 2018-04-27 10:56:29 -07:00
samples Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching 2018-04-20 08:51:55 -07:00
scripts drm-misc-next for v4.18: 2018-04-30 09:32:43 +10:00
security Merge branch 'userns-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-04-24 17:58:51 -07:00
sound ALSA: dice: fix error path to destroy initialized stream data 2018-04-26 15:24:54 +02:00
tools Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-29 09:36:22 -07:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM fixes for v4.17-rc3 2018-04-27 16:13:31 -07:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge candidates for 4.17 merge window 2018-04-06 17:35:43 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Merge remote-tracking branch 'drm/drm-next' into drm-misc-next 2018-05-11 18:08:10 +02:00
Makefile Linux v4.17-rc3 2018-04-29 14:17:42 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

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.
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.