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When DMA Rx completes, the current behavior is to just exit the DMA completion handler without future actions. If the transfer is still on-going, UART will trigger an interrupt and that eventually rearms the DMA Rx. The extra interrupt round-trip has an inherent latency cost that increases the risk of FIFO overrun. In such situations, the latency margin tends to already be less due to FIFO not being empty. Add check into DMA Rx completion handler to detect if LSR has DR (Data Ready) still set. DR indicates there will be more characters pending and DMA Rx can be rearmed right away to handle them. Cc: Gilles BULOZ <gilles.buloz@kontron.com> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://lore.kernel.org/r/20221107102126.56481-1-ilpo.jarvinen@linux.intel.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.