linux-kernel - Re: [PATCH v3 09/10] dt-bindings: pinctrl: stm32: Support I/O synchronization parameters

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Message-ID: <9dfdf02b7e5a99c515aff3c6528e2d5f70517201.camel@foss.st.com>
Date: Tue, 21 Oct 2025 13:49:35 +0200
From: Antonio Borneo <antonio.borneo@...s.st.com>
To: Linus Walleij <linus.walleij@...aro.org>
CC: Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>,
        "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "Maxime
 Coquelin" <mcoquelin.stm32@...il.com>,
        Alexandre Torgue
	<alexandre.torgue@...s.st.com>,
        Bartosz Golaszewski <brgl@...ev.pl>, <linux-gpio@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Christophe Roullier
	<christophe.roullier@...s.st.com>,
        Fabien Dessenne
	<fabien.dessenne@...s.st.com>,
        Valentin Caron <valentin.caron@...s.st.com>
Subject: Re: [PATCH v3 09/10] dt-bindings: pinctrl: stm32: Support I/O
 synchronization parameters

On Tue, 2025-10-21 at 00:08 +0200, Linus Walleij wrote:
> On Mon, Oct 20, 2025 at 5:09 PM Antonio Borneo
> <antonio.borneo@...s.st.com> wrote:
> 
> > pinconf-generic only accepts positive numeric values for
> > both generic and custom properties in struct pinconf_generic_params.
> 
> Do you need it to support negative values?

No, the point is not the sign, but the value that has to be numeric. More details below.

> Patches welcome!
> 
> > Plus, I haven't found any existing driver that mixes pinconf-generic with
> > custom string values.
> 
> Maybe I misunderstand, but pinconf_generic_parse_dt_config()
> looks at  pctldev->desc->custom_params and
> pctldev->desc->num_custom_params found in
> struct pinctrl_desc in
> include/linux/pinctrl/pinctrl.h

The issue is that parse_dt_cfg(), called by the above mentioned pinconf_generic_parse_dt_config(), only uses of_property_read_u32() to get the value of the property.
Conor's proposal for replacing my
st,io-sync = <0>;
with
st,io-sync = "pass-through";
doesn't fit in!

For my use case I'm going to extend parse_dt_cfg() with fwnode_property_match_property_string() to extract the index from an array of strings.
Then such index would be used for pinconf_to_config_packed().
Does this approach look reasonable?

I will send out the series shortly, after some test.

Regards,
Antonio