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d61ad23cb3When GPIO chip-select is used nothing prevents any available SPI controllers to work with both CS-high and traditional CS-low modes. In fact the SPI bus core code already does it, so we don't need to introduce any modification there. But spi_setup() still fails to switch the interface settings if CS-high flag is set for the case of GPIO-driven slave chip-select when the SPI controller doesn't support the hardwired CS-inversion. Lets fix it by clearing the SPI_CS_HIGH flag out from bad_bits (unsupported by controller) when client chip is selected by GPIO. This feature is useful for slave devices, which in accordance with communication protocol can work with both active-high and active-low chip-selects. I am aware of one such device. It is MMC-SPI interface, when at init sequence the driver needs to perform a read operation with low and high chip-select sequentially (requirement of 74 clock cycles with both chipselect, see the mmc_spi driver for details). Signed-off-by: Serge Semin <fancer.lancer@gmail.com> Signed-off-by: Mark Brown <broonie@kernel.org> |
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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.