I'm currently working on implementing SCMI pinctrl/gpio drivers on U-Boot[1]. Although the pinctrl driver for the kernel[2] was submitted by EPAM, it doesn't contain the gpio driver and I believe that we should discuss a couple of points on the kernel side to finalize my design for U-Boot. So this RFC is intended for reviews, especially to raise some issues. (Please note that I have *never* tested the code because I don't have any real hardware to test SCMI on it.) 1) how to obtain a value on an input pin All the existing gpio drivers are set to obtain a value on an input pin by accessing the hardware directly. In SCMI case, however, this is just impossible in its nature and must be supported via a protocol using "Input-value" configuration type. (See the spec[3], table-23.) The current pinconf framework is missing the feature (the pinconf parameter and a helper function). See patch#1 and #2. Please note that there is an issue around the pin configuration in EPAM's current pinctrl driver as I commented[4]. 2) DT bindings I would like to propose a generic binding for SCMI pinctrl based gpio driver. This allows a "consumer" driver to handle gpio input pins like as other normal gpio controllers provide. (patch#4) 3) generic GPIO driver Based on (2), I tried to prototype a generic driver in patch#3. As you can see, there is no SCMI-specific line of code as a set of existing helper functions, except (1), seem to be enough to implement required interfaces. So I'm not sure whether the driver should has a "compatibles" property of "arm,scmi-gpio-generic". I will appreciate any comments. -Takahiro Akashi [1] https://lists.denx.de/pipermail/u-boot/2023-September/529765.html [2] https://lkml.iu.edu/hypermail/linux/kernel/2308.1/01082.html [3] https://developer.arm.com/documentation/den0056/ [4] https://lkml.iu.edu/hypermail/linux/kernel/2308.2/07483.html AKASHI Takahiro (4): pinctrl: define PIN_CONFIG_INPUT pinctrl: add pinctrl_gpio_get_config() gpio: scmi: add SCMI pinctrl based gpio driver dt-bindings: gpio: Add bindings for SCMI pinctrl based gpio .../bindings/gpio/arm,scmi-gpio.yaml | 71 ++++++++ drivers/gpio/Kconfig | 8 + drivers/gpio/Makefile | 1 + drivers/gpio/gpio-scmi.c | 154 ++++++++++++++++++ drivers/pinctrl/core.c | 19 +++ include/linux/pinctrl/consumer.h | 8 + include/linux/pinctrl/pinconf-generic.h | 3 + 7 files changed, 264 insertions(+) create mode 100644 Documentation/devicetree/bindings/gpio/arm,scmi-gpio.yaml create mode 100644 drivers/gpio/gpio-scmi.c -- 2.34.1
