[RFC 0/4] gpio: add SCMI pinctrl based driver

AKASHI Takahiro
2023-10-02T02:17:14Z

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

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