linux-kernel - Re: [RFC PATCH 1/2] of: Add a variant of of_device_is_compatible() that can be build time culled

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Message-ID: <CAD++jL=fM8QL-cYwRTWNetUsoWoKUOEcxE2+6VYQ4o50F-H1PQ@mail.gmail.com>
Date: Sun, 11 Jan 2026 11:59:15 +0100
From: Linus Walleij <linusw@...nel.org>
To: Daniel Palmer <daniel@...ngy.jp>
Cc: Rob Herring <robh@...nel.org>, brgl@...nel.org, saravanak@...nel.org, 
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] of: Add a variant of of_device_is_compatible()
 that can be build time culled

Hi Daniel,

thanks for your patch!

I like the idea in this patch set. Footprint is something we need
to think more about, if for nothing else so for the increasing tendency
of RAM prices.

On Fri, Jan 9, 2026 at 3:52 AM Daniel Palmer <daniel@...ngy.jp> wrote:
> On Fri, 9 Jan 2026 at 08:38, Rob Herring <robh@...nel.org> wrote:
> >
> > On Wed, Jan 07, 2026 at 12:07:30PM +0900, Daniel Palmer wrote:
> > > In a lot of places we are using of_device_is_compatible() to check for quirks
> >
> > I'm assuming 'a lot' is not just 3 places? Got a rough estimate?
> >
> > This seems fine to me assuming there are more.
>
> In core code (like the gpio core, and not in a specific driver) there
> are only a few places. I think around 10.

Actually, if you look in gpiolib-of.c in e.g. of_gpio_try_fixup_polarity()
you find:

#if IS_ENABLED(CONFIG_LCD_HX8357)
                /*
                 * Himax LCD controllers used incorrectly named
                 * "gpios-reset" property and also specified wrong
                 * polarity.
                 */
                { "himax,hx8357",       "gpios-reset",  false },
                { "himax,hx8369",       "gpios-reset",  false },
#endif

etc etc etc.

It is actually a similar idea just clunkier, but maybe necessary
for these quirks since they are in a table.

But as you can see, there is some of the same thinking: if it's
not configured in, then we need to compile it out.

Yours,
Linus Walleij