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The Playback/Capture ctl currently reports rate value set by USB control selector UAC2_CS_CONTROL_SAM_FREQ (fixed for UAC1). When the stops playback/capture, the reported value does not change. The gadget side has no information whether the host has started/stopped capture/playback. This patch sets the value reported by the respective rate ctl to zero when the host side has stopped playback/capture. Also, it calls snd_ctl_notify when start/stop occurs, so that a subscribed client can act appropriately. Tests have confirmed that USB hosts change UAC2_CS_CONTROL_SAM_FREQ before switching altsetting to activate playback/capture, resulting in correct order (params->c/p_srate is set to requested rate before u_audio_start_capture/playback is called). The gadget rate notifications are used by user-space audio gadget controller gaudio_ctl https://github.com/pavhofman/gaudio_ctl. Signed-off-by: Pavel Hofman <pavel.hofman@ivitera.com> Link: https://lore.kernel.org/r/20220121155308.48794-8-pavel.hofman@ivitera.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.