linux-kernel - Re: [PATCH v4 2/9] dt-bindings: i2c: add bindings for i2c analog and digital filter

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Date:   Mon, 2 Sep 2019 16:22:51 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Eugen.Hristev@...rochip.com
Cc:     peda@...ntia.se, wsa@...-dreams.de, mark.rutland@....com,
        Ludovic.Desroches@...rochip.com, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, pierre-yves.mordret@...com,
        robh+dt@...nel.org
Subject: Re: [PATCH v4 2/9] dt-bindings: i2c: add bindings for i2c analog and
 digital filter

Eugen,

On 02/09/2019 14:15:14+0000, Eugen.Hristev@...rochip.com wrote:
> On 02.09.2019 13:49, Peter Rosin wrote:
> 
> > On 2019-09-02 12:12, Eugen.Hristev@...rochip.com wrote:
> >> From: Eugen Hristev <eugen.hristev@...rochip.com>
> >>
> >> Some i2c controllers have a built-in digital or analog filter.
> >> This is specifically required depending on the hardware PCB/board.
> >> Some controllers also allow specifying the maximum width of the
> >> spikes that can be filtered. The width length can be specified in nanoseconds.
> >>
> >> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> >> ---
> >>   Documentation/devicetree/bindings/i2c/i2c.txt | 11 +++++++++++
> >>   1 file changed, 11 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> >> index 44efafd..8dbff67 100644
> >> --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> >> +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> >> @@ -55,6 +55,17 @@ wants to support one of the below features, it should adapt the bindings below.
> >>   	Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C
> >>   	specification.
> >>   
> >> +- i2c-analog-filter
> >> +	Enable analog filter for i2c lines.
> >> +
> >> +- i2c-digital-filter
> >> +	Enable digital filter for i2c lines.
> >> +
> >> +- i2c-filter-width-ns
> >> +	Width of spikes which can be filtered by either digital or analog
> >> +	filters (i2c-analog-filtr or i2c-digital-filtr). This width is specified
> > 
> > filtr -> filter (two instances)
> > 
> > What if you want/need to have different bandwidth for the digital and analog
> > filters? After all, this is a generic binding...
> 
> For our needs, this is enough: the purpose of the filters is to avoid 
> noise on the lines, the noise is as big as it is for the digital and for 
> the analog filters, since we use an absolute measurement for them. So I 
> do not know how useful it would be to make a difference.
> 

You are adding generic properties so they have to be generic and not
tied to your particular use case.


-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com