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After the eMMC sleep command (CMD5) has been sent, the card start signals busy on the DAT0 line, which can be monitored to understand when it's allowed to proceed to power off the VCC regulator. When MMC_CAP_WAIT_WHILE_BUSY isn't supported by the host the DAT0 line isn't being monitored for busy completion, but instead we are waiting a fixed period of time. The time corresponds to the sleep timeout that is specified in the EXT_CSD register of the eMMC card. This is many cases suboptimal, as the timeout corresponds to the worst case scenario. To improve the situation add support for HW busy polling through the ->card_busy() host ops, when the host supports this. Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com> Acked-by: Avri Altman <avri.altman@wdc.com> Link: https://lore.kernel.org/r/20210504161222.101536-6-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.