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If the value/data associated with a control changes in SOF it will send a notification (SOF_IPC_GLB_COMP_MSG with SOF_IPC_COMP_GET_VALUE/DATA). We have support for binary volatile control type, but we might have features where enum/switch/volume changes. Re-implementing everything as volatile as well would be not much of a gain for several reasons: - volatile controls would do an IPC all the time, regardless if there is a need or not. - We still don't have notification which forces userspace to continuously poll. When such notification arrives we use snd_ctl_notify_one() to signal userspace about the change. The kernel is prepared for two types of notification: - the notification carries the new data for the control (num_elems != 0) The new value/data is copied to the control's local data - blank message about a change The new flag for the scontrol (comp_data_dirty) is set and when next time user space reads the value via the kcontrol's get callback we will refresh the control's local data from the firmware. Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com> Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com> Tested-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com> Link: https://lore.kernel.org/r/20210903114018.2962-1-peter.ujfalusi@linux.intel.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 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.