linux-kernel - Re: [PATCH] dt-bindings: pincfg-node: Add "input-schmitt" property

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Message-ID:
 <IA1PR20MB495307B0AA8CD7E6D48DEF0FBBA22@IA1PR20MB4953.namprd20.prod.outlook.com>
Date: Tue, 16 Jul 2024 14:50:54 +0800
From: Inochi Amaoto <inochiama@...look.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, 
	Inochi Amaoto <inochiama@...look.com>, Conor Dooley <conor@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, linux-gpio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: pincfg-node: Add "input-schmitt" property

On Tue, Jul 16, 2024 at 08:16:59AM GMT, Krzysztof Kozlowski wrote:
> On 16/07/2024 04:16, Inochi Amaoto wrote:
> > On Mon, Jul 15, 2024 at 05:19:41PM GMT, Conor Dooley wrote:
> >> On Mon, Jul 15, 2024 at 05:55:28PM +0800, Inochi Amaoto wrote:
> >>> On Mon, Jul 15, 2024 at 11:21:25AM GMT, Krzysztof Kozlowski wrote:
> >>>> On 14/07/2024 13:28, Inochi Amaoto wrote:
> >>>>> On Sophgo CV18XX platform, threshold strength of schmitt trigger can
> >>>>> be configured. As this standard property is already supported by the
> >>>>> common pinconf code. Add "input-schmitt" property in pincfg-node.yaml
> >>>>> so that other platforms requiring such feature can make use of this
> >>>>> property.
> >>>>>
> >>>>> Signed-off-by: Inochi Amaoto <inochiama@...look.com>
> >>>>> ---
> >>>>>  Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml | 4 ++++
> >>>>>  1 file changed, 4 insertions(+)
> >>>>>
> >>>>> diff --git a/Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml b/Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml
> >>>>> index d0af21a564b4..e838fcac7f2a 100644
> >>>>> --- a/Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml
> >>>>> +++ b/Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml
> >>>>> @@ -88,6 +88,10 @@ properties:
> >>>>>      description: disable input on pin (no effect on output, such as
> >>>>>        disabling an input buffer)
> >>>>>
> >>>>> +  input-schmitt:
> >>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
> >>>>> +    description: threshold strength for schmitt-trigger
> >>>>
> >>>> Strength in which units? This should have proper property name suffix.
> >>>>
> >>>
> >>> I think it should be mV. Using voltage may leads to decimal.
> >>
> >> The standard suffix for voltage is "-microvolts", so no issues with
> >> decimals :) And with a standard suffix, the $ref can be dropped.
> > 
> > Yeah, I have seen the "-microvolts", but I does not think add standard
> > suffix is a good idea, as "input-schmitt" is a standard pinconf attribute.
> > 
> > The only thing confused me is that the description of PIN_CONFIG_INPUT_SCHMITT 
> > in include/linux/pinctrl/pinconf-generic.h says it just uses an custom
> 
> You cannot add binding based on argument "I don't want to change kernel
> code", so sorry, but it does not really matter whatever pinctrl has
> undocumented.
> 

Yes, that is true. Even if not considering the kernel code,
I think adding something generic like "input-schmit-xxx" is 
useful as input schmitt trigger has threshold strength. And
if we want to configure it, it should have a value.

As the original "input-schmitt" seems to be meaningless, I
will take Conor's advice and add "input-schmitt-micorvolts"
attribute to handle this.

Regards,
Inochi