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The static config of the sja1105 switch is a long stream of bytes which is programmed to the hardware in chunks (portions with the chip select continuously asserted) of max 256 bytes each. Each chunk is a spi_message composed of 2 spi_transfers: the buffer with the data and a preceding buffer with the SPI access header. Only that certain SPI controllers, such as the spi-sc18is602 I2C-to-SPI bridge, cannot keep the chip select asserted for that long. The spi_max_transfer_size() and spi_max_message_size() functions are how the controller can impose its hardware limitations upon the SPI peripheral driver. For the sja1105 driver to work with these controllers, both buffers must be smaller than the transfer limit, and their sum must be smaller than the message limit. Regression-tested on a switch connected to a controller with no limitations (spi-fsl-dspi) as well as with one with caps for both max_transfer_size and max_message_size (spi-sc18is602). Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.