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In mmc_poll_for_busy() we loop continuously, either by sending a CMD13 or by invoking the ->card_busy() host ops, as to detect when the card stops signaling busy. This behaviour is problematic as it may cause CPU hogging, especially when the busy signal time reaches beyond a few ms. Let's fix the issue by adding a throttling mechanism, that inserts a usleep_range() in between the polling attempts. The sleep range starts at 32-64us, but increases for each loop by a factor of 2, up until the range reaches ~32-64ms. In this way, we are able to keep the loop fine-grained enough for short busy signaling times, while also not hogging the CPU for longer times. Note that, this change is inspired by the similar throttling mechanism that we already use for mmc_do_erase(). Reported-by: Michał Mirosław <mirq-linux@rere.qmqm.pl> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> Tested-by: Baolin Wang <baolin.wang7@gmail.com> Tested-by: Ludovic Barre <ludovic.barre@st.com> Reviewed-by: Ludovic Barre <ludovic.barre@st.com> Link: https://lore.kernel.org/r/20200204085449.32585-2-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.