linux-kernel - Re: [PATCH v7 1/3] dt-bindings: media: stm32-dcmi: Add DCMI min frequency property

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Message-ID: <20e4907a-f218-3e43-1111-7d4b9ee6d945@st.com>
Date:   Fri, 10 Jul 2020 07:33:40 +0000
From:   Benjamin GAIGNARD <benjamin.gaignard@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Hugues FRUCHET <hugues.fruchet@...com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "valentin.schneider@....com" <valentin.schneider@....com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 1/3] dt-bindings: media: stm32-dcmi: Add DCMI min
 frequency property



On 7/9/20 10:37 PM, Rob Herring wrote:
> On Wed, Jul 01, 2020 at 03:01:27PM +0200, Benjamin Gaignard wrote:
>> Document st,stm32-dcmi-min-frequency property which is used to
>> request CPUs minimum frequency when streaming frames.
>>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
>> ---
>>   Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> index 3fe778cb5cc3..05ca85a2411a 100644
>> --- a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> +++ b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
>> @@ -44,6 +44,13 @@ properties:
>>         bindings defined in
>>         Documentation/devicetree/bindings/media/video-interfaces.txt.
>>   
>> +  st,stm32-dcmi-min-frequency:
>> +    description: DCMI minimum CPUs frequency requirement (in KHz).
>> +    allOf:
>> +      - $ref: /schemas/types.yaml#/definitions/uint32
>> +      - minimum: 0
>> +      - default: 0
> I think this is questionable to be in DT and if it is, it's something
> that's hardly specific to ST or this block. IIRC, we already have a way
> to specify minimum OPPs.
This binding is only needed on some STM32 SoC when DVFS is activated
with low frequency setting in opp. The value also depends of the targeted
video format and framerate.

It is not an opp because it doesn't define a voltage-current-frequency 
combination
but only set a minimum target for the CPUs frequency to guaranty a good 
reaction
time when handling IRQs for the sensor.

Benjamin
>
> Rob