linux-kernel - Re: [PATCH v2 1/2] gpiolib: Fix a mess with the GPIO

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Date: Fri, 12 Apr 2024 10:20:24 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Kent Gibson <warthog618@...il.com>, 
	linux-gpio@...r.kernel.org, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org, 
	brcm80211@...ts.linux.dev, brcm80211-dev-list.pdl@...adcom.com, 
	Mika Westerberg <mika.westerberg@...ux.intel.com>, Bartosz Golaszewski <brgl@...ev.pl>, 
	Arend van Spriel <arend.vanspriel@...adcom.com>, Kalle Valo <kvalo@...nel.org>, 
	Charles Keepax <ckeepax@...nsource.cirrus.com>
Subject: Re: [PATCH v2 1/2] gpiolib: Fix a mess with the GPIO_* flags

On Tue, Apr 9, 2024 at 1:17 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:

> The GPIO_* flag definitions are *almost* duplicated in two files
> (with unmatches OPEN_SOURCE / OPEN_DRAIN). Moreover, some code relies
> on one set of definitions while the rest is on the other. Clean up
> this mess by providing only one source of the definitions to all.
>
> Fixes: b424808115cb ("brcm80211: brcmsmac: Move LEDs to GPIO descriptors")
> Fixes: 5923ea6c2ce6 ("gpio: pass lookup and descriptor flags to request_own")
> Fixes: fed7026adc7c ("gpiolib: Make use of enum gpio_lookup_flags consistent")
> Fixes: 4c0facddb7d8 ("gpio: core: Decouple open drain/source flag with active low/high")
> Fixes: 69d301fdd196 ("gpio: add DT bindings for existing consumer flags")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

The way the line lookup flags ("lflags") were conceived was through
support for non-DT systems using descriptor tables, and that is how
enum gpio_lookup_flags came to be.

When OF support was added it was bolted on on the side, in essence
assuming that the DT/OF ABI was completely separate (and they/we
sure like to think about it that way...) and thus needed translation from
OF flags to kernel-internal enum gpio_lookup_flags.

The way *I* thought about this when writing it was certainly that the
DT bindings was a separate thing (<dt-bindings/*.h> didn't even exist
at the time I think) and that translation from OF to kernel-internal
lflags would happen in *one* place.

The main reasoning still holds: the OF define is an ABI, so it can
*never* be changed, but the enum gpio_lookup_flags is subject to
Documentation/process/stable-api-nonsense.rst and that means
that if we want to swap around the order of the definitions we can.

But admittedly this is a bit over-belief in process and separation of
concerns and practical matters may be something else...

Yours,
Linus Walleij