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Add an ALSA control (CAL_DATA) that can be used to restore amp calibration, instead of using debugfs. A readback control (CAL_DATA_RB) is also added for factory testing. On ChromeOS the process that restores amp calibration from NVRAM has limited permissions and cannot access debugfs. It requires an ALSA control that it can write the calibration blob into. ChromeOS also restricts access to ALSA controls, which avoids the risk of accidental or malicious overwriting of good calibration data with bad data. As this control is not needed for normal Linux-based distros it is a Kconfig option. A separate control, CAL_DATA_RB, provides a readback of the current calibration data, which could be either from a write to CAL_DATA or the result of factory production-line calibration. The write and read are intentionally separate controls to defeat "dumb" save-and-restore tools like alsa-restore that assume it is safe to save all control values and write them back in any order at some undefined future time. Such behavior carries the risk of restoring stale or bad data over the top of good data. Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com> Link: https://patch.msgid.link/20251111130850.513969-3-rf@opensource.cirrus.com Signed-off-by: Mark Brown <broonie@kernel.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 reStructuredText 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.