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[Why] PSP doesn't have the ability to store SRM in a non-volatile memory. And since the kernel cannot write to the storage directly, we need usermode to facilitate this As per spec the SRM needs to be persistent so this interface is to be called by the usermode anytime the system goes down/powers on *boot/resume: load from storage *shutdown/suspend: save to storage [How] Provide a sysfs interface so that the usermode can set/get srm at the right times save to storage: call "cat /sys/class/drm/card0/device/hdcp_srm > file" after boot and resume -driver calls psp_get_srm() to get the stored srm and outputs it load from storage: call "cat file > /sys/class/drm/card0/device/hdcp_srm" before shutdown and suspend -driver reads the file from sysfs and calls psp_set_srm() to send the SRM to PSP v2: -update commit description -add comment about sysfs file handling in the code v3: - squash in use after free fix (Dan Carpenter) Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com> Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com> Reviewed-by: Harry Wentland <harry.wentland@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
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.