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During the card initialization process, the mmc core checks whether the eMMC/SD card supports an internal writeback-cache and then enables it inside the card. Unfortunately, this isn't according to what the mmc core reports to the upper block layer. Instead, the writeback-cache support with REQ_FLUSH and REQ_FUA, are being enabled depending on whether the host supports the CMD23 (MMC_CAP_CMD23) and whether an eMMC supports the reliable-write command. This is wrong and it may also sound awkward. In fact, it's a remnant from when both eMMC/SD cards didn't have dedicated commands/support to control the internal writeback-cache. In other words, it was the best we could do at that point in time. To fix the problem, but also without breaking backwards compatibility, let's align the REQ_FLUSH support with whether the writeback-cache became successfully enabled - for both eMMC and SD cards. Cc: stable@kernel.org Fixes:881d1c25f7("mmc: core: Add cache control for eMMC4.5 device") Fixes:130206a615("mmc: core: Add support for cache ctrl for SD cards") Depends-on:97fce126e2("mmc: block: Issue a cache flush only when it's enabled") Reviewed-by: Avri Altman <Avri.Altman@wdc.com> Signed-off-by: Michael Wu <michael@allwinnertech.com> Link: https://lore.kernel.org/r/20220331073223.106415-1-michael@allwinnertech.com [Ulf: Re-wrote the commit message] Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
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.