linux-kernel - Re: [PATCH] pinctrl: qcom: Fix behavior in abscense of open-drain support

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Date: Fri, 26 Apr 2024 23:18:30 -0700
From: Brian Norris <computersforpeace@...il.com>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
Cc: Johan Hovold <johan@...nel.org>, Bjorn Andersson <andersson@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Jaiganesh Narayanan <njaigane@...eaurora.org>, 
	Doug Anderson <dianders@...omium.org>, linux-arm-msm@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: qcom: Fix behavior in abscense of open-drain support

Hi Bjorn,

On Fri, Apr 26, 2024 at 4:44 PM Bjorn Andersson
<quic_bjorande@...cinc.com> wrote:
> On Fri, Apr 26, 2024 at 03:08:06PM -0700, Brian Norris wrote:
> > Apologies if I broke something here.
>
> False alarm on the breakage part, I got lost in the software layers.

OK! Glad it's not causing a visible problem.

> > But I can't tell based on subsequent conversation: are you observing a
> > real problem, or is this a theoretical one that only exists if the
> > gpiochip driver adds set_config() support?
> >
>
> There is a problem that if a non-ipq4019 device where to be pinconf'ed
> for open-drain, the outcome would be unexpected

Well as observed elsewhere, that's not permitted in most MSM bindings
;) But still might be nice to remove the landmine.

> and I have a concern
> that someone one day would implement set_config().
>
> So, I'd like to fix this, but my argumentation is at least wrong.

Sure.

I haven't surveyed the other pinconf types well, but how does this
driver handle all that? Are all other types supported uniformly by all
qcom pin blocks? It seems a little weird to be treating bit 0 as a
NULL choice, but clearly it works for now, with only a single non-zero
bit user.

> > https://git.kernel.org/linus/99d19f5a48ee6fbc647935de458505e9308078e3
>
> Perhaps we could convert that to yaml?

Ha, sure, perhaps. I don't have time for that soon, but there's a
chance such a patch could materialize in the future.

> Thank you for taking a look, Brian. This was valuable input. I will
> rework this to have a valid motivation - at least.

You're welcome! Glad it's cleared up enough to help move forward.

Regards,
Brian