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In the current code, there is no check at the stream open time whether the endpoint is being already used by others. In the normal operations, this shouldn't happen, but in the case of the implicit feedback mode, it's a common problem with the full duplex operation, because the capture stream is always opened by the playback stream as an implicit sync source. Although we recently introduced the check of such a conflict of parameters at the PCM hw_params time, it doesn't give any hint at the hw_params itself and just gives the error. This isn't quite comfortable, and it caused problems on many applications. This patch attempts to make the parameter handling easier by introducing the strict hw constraint matching with the counterpart stream that is being used. That said, when an implicit feedback playback stream is running before a capture stream is opened, the capture stream carries the PCM hw-constraint to allow only the same sample rate, format, periods and period frames as the running playback stream. If not opened or there is no conflict of endpoints, the behavior remains as same as before. Note that this kind of "weak link" should work for most cases, but this is no concrete solution; e.g. if an application changes the hw params multiple times while another stream is opened, this would lead to inconsistencies. Tested-by: Keith Milner <kamilner@superlative.org> Tested-by: Dylan Robinson <dylan_robinson@motu.com> Link: https://lore.kernel.org/r/20201123085347.19667-11-tiwai@suse.de Signed-off-by: Takashi Iwai <tiwai@suse.de> |
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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.