786115655f
Merge series from David Lechner <dlechner@baylibre.com>: This is a follow-up to [1] where it was suggested to break down the proposed SPI offload support into smaller series. This takes on the first suggested task of introducing an API to "pre-cook" SPI messages. This idea was first discussed extensively in 2013 [2][3] and revisited more briefly 2022 [4]. The goal here is to be able to improve performance (higher throughput, and reduced CPU usage) by allowing peripheral drivers that use the same struct spi_message repeatedly to "pre-cook" the message once to avoid repeating the same validation, and possibly other operations each time the message is sent. This series includes __spi_validate() and the automatic splitting of xfers in the optimizations. Another frequently suggested optimization is doing DMA mapping only once. This is not included in this series, but can be added later (preferably by someone with a real use case for it). To show how this all works and get some real-world measurements, this series includes the core changes, optimization of a SPI controller driver, and optimization of an ADC driver. This test case was only able to take advantage of the single validation optimization, since it didn't require splitting transfers. With these changes, CPU usage of the threaded interrupt handler, which calls spi_sync(), was reduced from 83% to 73% while at the same time the sample rate (frequency of SPI xfers) was increased from 20kHz to 25kHz. [1]: https://lore.kernel.org/linux-spi/20240109-axi-spi-engine-series-3-v1-1-e42c6a986580@baylibre.com/T/ [2]: https://lore.kernel.org/linux-spi/E81F4810-48DD-41EE-B110-D0D848B8A510@martin.sperl.org/T/ [3]: https://lore.kernel.org/linux-spi/39DEC004-10A1-47EF-9D77-276188D2580C@martin.sperl.org/T/ [4]: https://lore.kernel.org/linux-spi/20220525163946.48ea40c9@erd992/T/
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.