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All drivers in ALSA firewire stack have never reported extra delay for the runtime of PCM substream. There is some reason, but the main reason is that the meaning of extra delay differs depending on driver design, especially for the packet-oriented driver. Here I define the extra delay for the case of IEC 61883-1/6. It is the number of PCM frames transferred or should be transferred between the current isochronous cycle and the isochronous cycle to which the latest isochronous packet arrived (in IR context) or is scheduled (in IT context). A commitbaa914cd81("firewire: add kernel API to access CYCLE_TIME register") allow unit drivers to read CYCLE_TIME of 1394 OHCI controller. It allows the drivers to compute the current isochronous cycle. Additionally, a commitf011712887("ALSA: firewire-lib: keep history to process isochronous packet") enables to save the history processing packets. It allows the driver to estimate the total number of data blocks in packets arriving shortly, or calculate the total number of data blocks in scheduled packets. Now it is ready. This commit implements the computation of the extra delay. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Link: https://lore.kernel.org/r/20230110134933.322794-4-o-takashi@sakamocchi.jp Signed-off-by: Takashi Iwai <tiwai@suse.de>
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.