linux-kernel - Re: [PATCH v2 1/2] dt-bindings: i2c: snps,designware-i2c: add bus-capacitance-pf and clk-freq-optimized

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Message-ID:
 <IA1PR14MB622419FD28CA5E7679A040B98A742@IA1PR14MB6224.namprd14.prod.outlook.com>
Date: Sat, 28 Sep 2024 07:07:34 +0000
From: Michael Wu <Michael.Wu@...ron.us>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: Andi Shyti <andi.shyti@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Mika Westerberg
	<mika.westerberg@...ux.intel.com>, Jan Dabros <jsd@...ihalf.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, morgan chang
	<morgan.chang@...ron.us>, "mvp.kutali@...il.com" <mvp.kutali@...il.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: i2c: snps,designware-i2c: add
 bus-capacitance-pf and clk-freq-optimized

On Fri, Sep 27 2024 at 10:35:09AM +0200, Krzysztof Kozlowski wrote:
> On Fri, Sep 27, 2024 at 12:22:16PM +0800, Michael Wu wrote:
...
> > index 60035a787e5c..fc19e6a8b306 100644
> > --- a/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml
> > +++ b/Documentation/devicetree/bindings/i2c/snps,designware-i2c.yaml
> > @@ -87,6 +87,20 @@ properties:
> >        This value is used to compute the tHIGH period.
> >      default: 300
> >
> > +  bus-capacitance-pf:
> 
> Why is this generic property? Is this going to be applied to all I2C
> controllers? If not, you miss vendors prefix.
>
> > +    description: |
> > +      This property represents the bus capacitance in picofarad (pF). It
> > +      affects the high and low pulse width of SCL line in high speed mode.
> > +      The only legal values for this property are 100 and 400, which are
> used
> > +      to calculate the tHIGH and tLOW periods for high speed mode.
> > +    default: 100
> > +
> > +  clk-freq-optimized:
> 
> This was never tested.
> 
> You got this comment already and not much improved.
> 
> It does not look like you tested the bindings, at least after quick
> look. Please run  (see
> Documentation/devicetree/bindings/writing-schema.rst for instructions).
> Maybe you need to update your dtschema and yamllint.
> 
> > +    description: |
> 
> Do not need '|' unless you need to preserve formatting.
> 
> Missing vendor prefix. Missing tests.
> 
> Also, extend the example with this.
> 

Both are snps,designware-i2c properties, and should be renamed to
snps,bus-capacitance-pf and snps,clk-freq-optimized.

I apologize for my lack of understanding of binding.

> 
> > +      If the hardware input clock frequency is reduced by reducing the
> > +      internal latency, this property must be declared in the device tree. It
> > +      affects the high period and low period of SCL line.
> 
> I assume this is hardware choice, not driver?

Yes, they are hardware properties. The driver must use this information
from the device tree to calculate SCL high and low periods appropriate
for the hardware.

Thanks & Regards,
Michael