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The STM32 DMA doesn't have the ability to generate convenient burst transfer on the DDR, ensuring the best load of the AXI & DDR. To avoid this bad load of the AXI & DDR, STM32 MDMA can be used to transfer data to the DDR, being triggered by STM32 DMA channel transfer completion. An SRAM buffer is used between DMA and MDMA. So the MDMA always does MEM_TO_MEM transfers (from/to SRAM to/from DDR), and the DMA uses SRAM instead of DDR with DEV_TO_MEM transfers. SPI RX DMA (DEV_TO_MEM) becomes: SPI RX FIFO ==DMA==> SRAM ==MDMA==> DDR In RX (DEV_TO_MEM), EOT interrupt is used to pause the DMA channel (which will raise a transfer complete) to trigger the MDMA to flush the SRAM (when transfer length is not aligned on SRAM period). TX remains on the former implementation. Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com> Link: https://patch.msgid.link/20250616-spi-upstream-v1-4-7e8593f3f75d@foss.st.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 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.