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Some busses, like I2C, strictly need to have the line handled as open drain, i.e. not actively driven high. For this reason the i2c-gpio.c bit-banged I2C driver is reimplementing open drain handling outside of gpiolib. This is not very optimal. Instead make it possible for a consumer to explcitly express that the line must be handled as open drain instead of allowing local hacks papering over this issue. The descriptor tables, whether DT, ACPI or board files, should of course have flagged these lines as open drain. E.g.: enum gpio_lookup_flags GPIO_OPEN_DRAIN for a board file, or gpios = <&foo 42 GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN>; in a device tree using <dt-bindings/gpio/gpio.h> But more often than not, these descriptors are wrong. So we need to make it possible for consumers to enforce this open drain behaviour. We now have two new enumerated GPIO descriptor config flags: GPIOD_OUT_LOW_OPEN_DRAIN and GPIOD_OUT_HIGH_OPEN_DRAIN that will set up the lined enforced as open drain as output low or high, using open drain (if the driver supports it) or using open drain emulation (setting the line as input to drive it high) from the gpiolib core. Cc: linux-gpio@vger.kernel.org Tested-by: Geert Uytterhoeven <geert+renesas@glider.be> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.