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Consider the following scenario:
1. nonblocking enable crtc
2. wait for the event
3. nonblocking disable crtc
On i915 this can lead to a spurious -EBUSY from step 3 on
account of non-enabled planes getting the fake_commit in step 1
and we don't complete the fake_commit-> flip_done until
drm_atomic_helper_commit_hw_done() which can happen a long
time after the flip event was sent out.
This will become somewhat easy to hit on SKL+ once we start
to add all the planes for the crtc to every modeset commit
for the purposes of forcing a watermark register programming
[1].
To make the race a little less pronounced let's complete
fake_commit->flip_done after drm_atomic_helper_wait_for_flip_done().
For the single crtc case this should make the race quite
theoretical, assuming drm_atomic_helper_wait_for_flip_done()
actually has to wait for the real commit flip_done. In case
the real commit flip_done gets completed singificantly before
drm_atomic_helper_wait_for_flip_done(), or we are dealing with
multiple crtcs whose vblanks don't line up nicely the race still
exists.
[1] https://patchwork.freedesktop.org/patch/262670/
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.