Re: [PATCH RESEND 1/2] arm64: dts: rockchip: rk3308: Add gpio-ranges properties

[Matthijs Kooijman <matthijs@stdin.nl>]

[-- Attachment #1: Type: text/plain, Size: 1357 bytes --]

Hey Linus,

> We do not like it when people depend on the global GPIO numbering.

Yeah, I know. That's also why this patch is useful: It stops relying on
global numbering for auto-defining gpio-ranges and instead defines them
explicitly (for this particular DT at least).

Looking at the code (rockchip_gpiolib_register()), I do think it could
be rewritten to use dynamic GPIO numbering (since the same code
currently sets gc->base based on the bank->pin_base, and then defines
gpio-ranges based on gc->base, but I think it could just use
bank->pin_base directly and *not* set gc->base at all to use dynamic
numbering). However, actually making such invasive changes is out of
scope (and time budget) for me :-)

> > but I see in the code that
> > GPIO drivers decide themselves (by setting gc->base statically or maybe
> > based on DT).
>
> They *can* but they really shouldn't. This mechanism exists for
> legacy reasons.

I did read this comment today:

	/* dynamic allocation of GPIOs, e.g. on a hotplugged device */
	static int gpiochip_find_base_unlocked(u16 ngpio)

Which suggested to me that static allocation was still the recommended
default and dynamic allocation primarily used for cases where static
allocation cannot work (like hotplug). But your messages suggests that
static allocation is discouraged more actively than that.

Gr.

Matthijs

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]