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Linux kernel source tree
d3fb9a24a6
Currently, the doorbell is written to and a wmb() is used to commit it
immediately.
wmb() ensures that the write completes before following writes occur, but
completion doesn't mean that it isn't stored in a buffer somewhere. The
recommendation for ensuring this bit has taken effect on the device is to
perform a read back to force it to make it all the way to the device. This
is documented in device-io.rst and a talk by Will Deacon on this can be
seen over here:
https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678
But, completion and taking effect aren't necessary to guarantee here.
There's already other examples of the doorbell being rung that don't do
this. The writel() of the doorbell guarantees prior writes by this thread
(to the request being setup for example) complete prior to the ringing of
the doorbell, and the following wait_for_completion_io_timeout() doesn't
require any special memory barriers either.
With that in mind, just remove the wmb() altogether here.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| 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 reStructuredText 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.