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When the SPI QUP controller is used together with a DMA engine it needs to vote for the interconnect path to the DRAM. Otherwise it may be unable to access the memory quickly enough. The requested peak bandwidth is dependent on the SPI core/bus clock so that the bandwidth scales together with the selected SPI speed. To avoid sending votes too often the bandwidth is always requested when a DMA transfer starts, but dropped only on runtime suspend. Runtime suspend should only happen if no transfer is active. After resumption we can defer the next vote until the first DMA transfer actually happens. Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com> Link: https://lore.kernel.org/r/20230919-spi-qup-dvfs-v2-4-1bac2e9ab8db@kernkonzept.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 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.