linux-kernel - Re: [PATCH v2 1/2] driver core: Export device_is

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Message-ID: <CAMRc=MdhG7tBoEt2cm8qVJS8tisKPNr6u+umtPW6dFw8yF=N=A@mail.gmail.com>
Date: Thu, 4 Dec 2025 11:14:04 +0100
From: Bartosz Golaszewski <brgl@...nel.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Maxime Ripard <mripard@...nel.org>, rafael@...nel.org, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linux-next@...r.kernel.org, 
	sfr@...b.auug.org.au, andrzej.hajda@...el.com, neil.armstrong@...aro.org, 
	rfoss@...nel.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se, 
	jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com, 
	tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch, 
	angelogioacchino.delregno@...labora.com, ulf.hansson@...aro.org, 
	linus.walleij@...aro.org, Liu Ying <victor.liu@....com>
Subject: Re: [PATCH v2 1/2] driver core: Export device_is_dependent() to modules

On Wed, Dec 3, 2025 at 6:01 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > I hope that explains it better.
>
> Yes it does, thanks.
>
> > To answer your question: the caller can't tell GPIO about this relationship,
> > GPIO would have to ask reset about it but having a dedicated symbol for this
> > doesn't really sound like the best approach.
>
> Ah, ick, no it doesn't.  I really don't know what to suggest here,
> sorry.
>

I found a viable workaround inside GPIO where I create another GPIO
shared proxy for the potential reset-gpio device. So that if there are
two users of the same "reset-gpios", we create three proxies in total:
one for user 1, one for user 2 and another one for the reset-gpio
device which may or may not be instantiated.

I think that the best approach would still be having access to
device_is_dependent(). I don't quite get why read-only inspecting
device links outside of PM or driver core should really be a bad
thing, but I can live without it, I guess.

Bart