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When source data width/burst and destination data width/burst are different, data are packed or unpacked in DMA3 channel FIFO. Data are pushed out from DMA3 channel FIFO when the destination burst length (= data width * burst) is reached. If the channel is stopped before the transfer end, and if some bytes are packed/unpacked in the DMA3 channel FIFO, these bytes are lost. Indeed, DMA3 channel FIFO has no flush capability, only reset. To avoid potential bytes lost, pack/unpack must be prevented by setting memory data width/burst equal to peripheral data width/burst. Memory accesses will be penalized. But it is the only way to avoid bytes lost. Some devices (e.g. cyclic RX like UART) need this, so add the possibility to prevent pack/unpack feature, by setting bit 16 of the 'DMA transfer requirements' bit mask. Acked-by: Rob Herring (Arm) <robh@kernel.org> Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com> Link: https://lore.kernel.org/r/20241016-dma3-mp25-updates-v3-1-8311fe6f228d@foss.st.com Signed-off-by: Vinod Koul <vkoul@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 reStructuredText 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.