linux-kernel - Re: [PATCH v3 1/8] dt-bindings: clock: imx8m-clock: support spread spectrum clocking

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Message-ID: <b7c1499b-8337-421c-9734-6e518d678ff8@kernel.org>
Date: Wed, 6 Nov 2024 15:13:37 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc: linux-kernel@...r.kernel.org, linux-amarula@...rulasolutions.com,
 Abel Vesa <abelvesa@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Fabio Estevam <festevam@...il.com>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Michael Turquette <mturquette@...libre.com>,
 Peng Fan <peng.fan@....com>, Pengutronix Kernel Team
 <kernel@...gutronix.de>, Rob Herring <robh@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>, Shawn Guo <shawnguo@...nel.org>,
 Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-clk@...r.kernel.org
Subject: Re: [PATCH v3 1/8] dt-bindings: clock: imx8m-clock: support spread
 spectrum clocking

On 06/11/2024 15:10, Krzysztof Kozlowski wrote:
> On Wed, Nov 06, 2024 at 09:57:57AM +0100, Dario Binacchi wrote:
>> The patch adds the DT bindings for enabling and tuning spread spectrum
>> clocking generation.
> 
> We had long talks about this but nothing of it got reflected in commit
> msg. Sorry, I don't remember what I was talking in some particular patch
> month ago, so you will get the same questions over and over...
> 
>>
>> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
>>
>> ---
>>
>> Changes in v3:
>> - Added in v3
>> - The dt-bindings have been moved from fsl,imx8m-anatop.yaml to
>>   imx8m-clock.yaml. The anatop device (fsl,imx8m-anatop.yaml) is
>>   indeed more or less a syscon, so it represents a memory area
>>   accessible by ccm (imx8m-clock.yaml) to setup the PLLs.
>>
>>  .../bindings/clock/imx8m-clock.yaml           | 46 +++++++++++++++++++
>>  1 file changed, 46 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> index c643d4a81478..7920393e518e 100644
>> --- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> +++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> @@ -43,6 +43,40 @@ properties:
>>        ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8m-clock.h
>>        for the full list of i.MX8M clock IDs.
>>  
>> +  fsl,ssc-clocks:
>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
>> +    description:
>> +      Phandles of the PLL with spread spectrum generation hardware capability.
>> +    minItems: 1
>> +    maxItems: 4
> 
> 1. How is it possible that you change spread spectrum of some clocks from
> main Clock Controller, while this device is not a consumer of them?
> Basically this means that this device does not have these clocks but yet
> you claim that it needs to configure spread for them! It's contradictory
> to me and nohing got explained in commit msg about it. I am pretty sure
> I asked about this alrady.

I digged my previous answer and it was pretty clear here:

18:44 <krzk> You can, but I still have the same concerns. How this
device - which does not take any clock input, has no clocks at all - can
depend on spread spectrum of some PLLs? Thsi device does not have clocks.
18:50 <krzk> device has no clocks, I checked now third time
18:50 <krzk> If device has clocks, it must have clocks property

So again, you do not need this property at all. I repeated it multiple
times - you are supposed to use clocks property.

> 
> 2. Why is this array flexible in size?
> 
> Best regards,
> Krzysztof
> 

Best regards,
Krzysztof