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A few of the I2C GPIO expander chips supported by this binding have a RESETN pin to be able to reset the chip. The chip is held in reset while the pin is low, therefore the polarity of reset-gpios is expected to reflect that, i.e. a GPIO_ACTIVE_HIGH means the GPIO will be driven high for reset and then driven low, GPIO_ACTIVE_LOW means the GPIO will be driven low for reset and then driven high. If a GPIO is directly routed to RESETN pin on the IC without any inverter, GPIO_ACTIVE_LOW is thus expected. Out of the supported chips, only PCA9670, PCA9671, PCA9672 and PCA9673 show a RESETN pin in their datasheets. They all share the same reset timings, that is 4+us reset pulse[0] and 100+us reset time[0]. When performing a reset, "The PCA9670 registers and I2C-bus state machine will be held in their default state until the RESET input is once again HIGH."[1] meaning we now know the state of each line controlled by the GPIO expander. Therefore, setting lines-initial-states and reset-gpios both does not make sense and their presence is XOR'ed. [0] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf Fig 22. [1] https://www.nxp.com/docs/en/data-sheet/PCA9670.pdf 8.5 Tested-by: Heiko Stuebner <heiko@sntech.de> # exclusion logic Acked-by: Conor Dooley <conor.dooley@microchip.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de> Link: https://lore.kernel.org/r/20250224-pca976x-reset-driver-v3-1-58370ef405be@cherry.de Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.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 reStructuredText 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.