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As per the spi core implementation for MSPI devices when the transfer is the last one in the message, the chip may stay selected until the next transfer. On multi-device SPI busses with nothing blocking messages going to other devices, this is just a performance hint; starting a message to another device deselects this one. But in other cases, this can be used to ensure correctness. Some devices need protocol transactions to be built from a series of spi_message submissions, where the content of one message is determined by the results of previous messages and where the whole transaction ends when the chipselect goes intactive. On CS change after completing the last serial transfer, the MSPI driver drives SSb pin CDRAM register correctly according comments in core spi.h as shown below: case 1) EOM =1, cs_change =0: SSb inactive case 2) EOM =1, cs_change =1: SSb active case 3) EOM =0, cs_change =0: SSb active case 4) EOM =0, cs_change =1: SSb inactive Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com> Link: https://lore.kernel.org/r/20200420190853.45614-5-kdasu.kdev@gmail.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.