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The driver supports several modes, one of them is PIO/IRQ "spi_imx_pio_transfer()". The data is exchanged with the IP core using PIO, an IRQ is setup to signal empty/full FIFOs and the end of the transfer. The IRQ and scheduling overhead for short transfers is significant. Using polling instead of IRQs can be beneficial to reduce the overall CPU load, especially on small transfer workloads. On an imx6 single core, a given RX workload of the mcp251xfd driver results in 40% CPU load. Using polling mode reduces the CPU load to 30%. This patch adds PIO polling support to the driver. For transfers with a duration of less than 30 µs the polling mode instead of IRQ based PIO mode is used. 30 µs seems to be a good compromise, which is used the by the SPI drivers for the raspberry Pi (spi-bcm2835, spi-bcm2835), too. Co-developed-by: David Jander <david@protonic.nl> Signed-off-by: David Jander <david@protonic.nl> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de> Link: https://lore.kernel.org/r/20220502175457.1977983-9-mkl@pengutronix.de 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.