Hi all, Hi Linus,
Linus, I've especially added you because you've expressed some concerns
about using bits and offsets in the device-tree [1].
I'd like to disuss adding a generic gpio-syscon (eg. compatible =
"gpio-syscon"). At the moment, if you have a board which could use the
gpio-syscon out-of-the-box, you still have to submit a patch to add
support to the gpio-syscon driver. Wouldn't it be easier to let the
user/board manufacturer configure the parameters through the dtb? I
understand your reasoning to have the information in two different
places, but isn't that alwas the case for any non trivial device tree
binding? On the other hand, if you'd have a generic gpio-syscon and the
actual hardware is compatible with it, all you have to do is to add the
devicetree fragment. You don't have to wait until your patch is approved
by the kernel maintainers, you don't have to wait until the kernel with
your patch actually makes it into the distributions, etc.
I have thought about something like:
gpio0 {
compatible = "gpio-syscon";
syscon = <&syscon>;
gpio-controller;
flags = <GPIO_SYSCON_FEAT_IN | GPIO_SYSCON_FEAT_OUT |
GPIO_SYSCON_FEAT_DIR>;
offsets = <0 0 1>;
io-width = <4>;
mask = <0x0000ffff>;
};
Where offsets is a tuple of (input register offset, output register
offset, direction register offset) and the driver would expose 16 GPIOs.
For the flags there might be something like:
#define GPIO_SYSCON_GPIO (GPIO_SYSCON_FEAT_IN | GPIO_SYSCON_FEAT_OUT |
GPIO_SYSCON_FEAT_DIR)
#define GPIO_SYSCON_GPI (GPIO_SYSCON_FEAT_IN)
#define GPIO_SYSCON_GPO (GPIO_SYSCON_FEAT_OUT)
TBH, I'm a newbie at what should be in the dts and what should be in the
driver, but I've seen the syscon-poweroff driver which can be used for
most use cases out-of-the-box.
-michael
[1]
https://www.mail-archive.com/linux-gpio@xxxxxxxxxxxxxxx/msg01660.html
