linux-kernel - Re: [PATCH 2/3] ASoC: dt-bindings: sama7g5-pdmc: add microchip,startup-delay-us binding

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Date:   Thu, 16 Feb 2023 10:41:20 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <krzysztof.kozlowski@...aro.org>, <lgirdwood@...il.com>,
        <broonie@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <lars@...afoo.de>,
        <perex@...ex.cz>, <tiwai@...e.com>, <Nicolas.Ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>
CC:     <alsa-devel@...a-project.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] ASoC: dt-bindings: sama7g5-pdmc: add
 microchip,startup-delay-us binding

On 16.02.2023 12:18, Krzysztof Kozlowski wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 16/02/2023 11:15, Claudiu.Beznea@...rochip.com wrote:
>> On 16.02.2023 12:04, Krzysztof Kozlowski wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> On 14/02/2023 17:14, Claudiu Beznea wrote:
>>>> Add microchip,startup-delay-us binding to let PDMC users to specify
>>>> startup delay.
>>>>
>>>> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
>>>> ---
>>>>  .../devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml   | 6 ++++++
>>>>  1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml b/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>>> index c4cf1e5ab84b..9b40268537cb 100644
>>>> --- a/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>>> +++ b/Documentation/devicetree/bindings/sound/microchip,sama7g5-pdmc.yaml
>>>> @@ -67,6 +67,12 @@ properties:
>>>>      maxItems: 4
>>>>      uniqueItems: true
>>>>
>>>> +  microchip,startup-delay-us:
>>>> +    description: |
>>>> +      Specifies the delay in microseconds that needs to be applied after
>>>> +      enabling the PDMC microphones to avoid unwanted noise due to microphones
>>>> +      not being ready.
>>>
>>> Is this some hardware delay? Or OS? If OS, why Linux specific delay is
>>> put into DT?
>>
>> It's the delay used in software workaround that IP needs to filter noises.
> 
> Then this sounds like OS? Linux related properties usually do not belong
> to DT.
> 
>> The IP is not fully featured to do this kind of filtering on its own thus
>> this software workaround. This delay may depend on used microphones thus
>> for different kind of setups (PDMC + different microphones) I introduced
>> this in DT.
> 
> I understand your driver needs delay and I am not questioning this. I am
> questioning why this is suitable for DT?

Because that delay may depend on the microphones that are used with PDMC.
Different boards may come with different microphones, thus the default
delay may not fit to fully filter the noise. Due to this I chose to add it
in DT.

> 
> 
> Best regards,
> Krzysztof
>