766c6b63aa
Commitf3186dd876("spi: Optionally use GPIO descriptors for CS GPIOs") introduced the optional use of GPIO descriptors for chip selects. A side-effect of this change: when a SPI bus uses GPIO descriptors, all its client devices have SPI_CS_HIGH set in spi->mode. This flag is required for the SPI bus to operate correctly. This unfortunately breaks many client drivers, which use the following pattern to configure their underlying SPI bus: static int client_device_probe(struct spi_device *spi) { ... spi->mode = SPI_MODE_0; spi->bits_per_word = 8; err = spi_setup(spi); .. } In short, many client drivers overwrite the SPI_CS_HIGH bit in spi->mode, and break the underlying SPI bus driver. This is especially true for Freescale/NXP imx ecspi, where large numbers of spi client drivers now no longer work. Proposed fix: ------------- When using gpio descriptors, depend on gpiolib to handle CS polarity. Existing quirks in gpiolib ensure that this is handled correctly. Existing gpiolib behaviour will force the polarity of any chip-select gpiod to active-high (if 'spi-active-high' devicetree prop present) or active-low (if 'spi-active-high' absent). Irrespective of whether the gpio is marked GPIO_ACTIVE_[HIGH|LOW] in the devicetree. Loose ends: ----------- If this fix is applied: - is commit138c9c32f0("spi: spidev: Fix CS polarity if GPIO descriptors are used") still necessary / correct ? Fixes:f3186dd876("spi: Optionally use GPIO descriptors for CS GPIOs") Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com> Acked-by: Linus Walleij <linus.walleij@linaro.org> Link: https://lore.kernel.org/r/20201106150706.29089-1-TheSven73@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.