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

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Message-ID: <b6528812-65d3-6561-38e7-c0545af900d8@microchip.com>
Date:   Mon, 2 Sep 2019 14:15:14 +0000
From:   <Eugen.Hristev@...rochip.com>
To:     <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>,
        <alexandre.belloni@...tlin.com>, <robh+dt@...nel.org>
Subject: Re: [PATCH v4 2/9] dt-bindings: i2c: add bindings for i2c analog and
 digital filter

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...

Hi Peter,

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.

Wolfram, what do you think ?

Eugen

> 
> Cheers,
> Peter
> 
>> +	in nanoseconds.
>> +
>>   - interrupts
>>   	interrupts used by the device.
>>   
>>
> 
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> 
> 

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