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ff369d7b98
During board verification, there is a need to test the various supported eMMC/SD speed modes. However, since the framework chooses the best mode supported by the card and the host controller's caps, this currently necessitates changing the devicetree for every iteration. Allow the various speed mode host capabilities to be modified via debugfs in order to allow easier hardware verification. The values to be written are the raw MMC_CAP* values from include/linux/mmc/host.h. This is rather low-level, and these defines are not guaranteed to be stable, but it is perhaps good enough for the intended use case. MMC_CAP_AGGRESSIVE_PM can also be set, in order to be able to re-initialize the card without having to physically remove and re-insert it. /sys/kernel/debug/mmc0# grep timing ios timing spec: 9 (mmc HS200) // Turn on MMC_CAP_AGGRESSIVE_PM and re-trigger runtime suspend /sys/kernel/debug/mmc0# echo $(($(cat caps) | (1 << 7))) > caps /sys/kernel/debug/mmc0# echo on > /sys/bus/mmc/devices/mmc0\:0001/power/control /sys/kernel/debug/mmc0# echo auto > /sys/bus/mmc/devices/mmc0\:0001/power/control // MMC_CAP2_HS200_1_8V_SDR /sys/kernel/debug/mmc0# echo $(($(cat caps2) & ~(1 << 5))) > caps2 /sys/kernel/debug/mmc0# echo on > /sys/bus/mmc/devices/mmc0\:0001/power/control /sys/kernel/debug/mmc0# grep timing ios timing spec: 8 (mmc DDR52) Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> Link: https://lore.kernel.org/r/20230929-mmc-caps-v2-2-11a4c2d94f15@axis.com Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> |
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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.