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Date:   Tue, 29 Mar 2022 13:57:33 +0530
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From:   Sameer Pujar <spujar@nvidia.com>
Subject: Re: [RFC PATCH v2 3/6] ASoC: dt-bindings: Extend clock bindings of
 rt5659
To:     Krzysztof Kozlowski <krzk@kernel.org>, broonie@kernel.org,
        lgirdwood@gmail.com, robh+dt@kernel.org, krzk+dt@kernel.org,
        perex@perex.cz, tiwai@suse.com, peter.ujfalusi@linux.intel.com,
        pierre-louis.bossart@linux.intel.com
Cc:     oder_chiou@realtek.com, thierry.reding@gmail.com,
        jonathanh@nvidia.com, alsa-devel@alsa-project.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-tegra@vger.kernel.org
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On 28-03-2022 18:58, Krzysztof Kozlowski wrote:
> On 28/03/2022 15:19, Sameer Pujar wrote:
>> On 28-03-2022 13:37, Krzysztof Kozlowski wrote:
>>> On 28/03/2022 09:58, Sameer Pujar wrote:
>>>> On 28-03-2022 12:36, Krzysztof Kozlowski wrote:
>>>>> External email: Use caution opening links or attachments
>>>>>
>>>>>
>>>>> On 28/03/2022 08:14, Sameer Pujar wrote:
>>>>>> The rt5658 or rt5659 CODEC system clock (SYSCLK) can be derived from
>>>>>> various clock sources. For example it can be derived either from master
>>>>>> clock (MCLK) or by internal PLL. The internal PLL again can take input
>>>>>> clock references from bit clocks (BCLKs) and MCLK. To enable a flexible
>>>>>> clocking configuration the DT binding is extended here.
>>>>>>
>>>>>> It makes use of standard clock bindings and sets up the clock relation
>>>>>> via DT.
>>>>>>
>>>>>> Signed-off-by: Sameer Pujar<spujar@nvidia.com>
>>>>>> Cc: Oder Chiou<oder_chiou@realtek.com>
>>>>>> ---
>>>>>>     .../devicetree/bindings/sound/realtek,rt5659.yaml  | 53 ++++++++++++++++++++--
>>>>>>     1 file changed, 49 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/sound/realtek,rt5659.yaml b/Documentation/devicetree/bindings/sound/realtek,rt5659.yaml
>>>>>> index b0485b8..0c2f3cb 100644
>>>>>> --- a/Documentation/devicetree/bindings/sound/realtek,rt5659.yaml
>>>>>> +++ b/Documentation/devicetree/bindings/sound/realtek,rt5659.yaml
>>>>>> @@ -29,12 +29,28 @@ properties:
>>>>>>         maxItems: 1
>>>>>>
>>>>>>       clocks:
>>>>>> -    items:
>>>>>> -      - description: Master clock (MCLK) to the CODEC
>>>>>> +    description: |
>>>>>> +      CODEC can receive multiple clock inputs like Master
>>>>>> +      clock (MCLK), I2S bit clocks (BCLK1, BCLK2, BCLK3,
>>>>>> +      BCLK4). The CODEC SYSCLK can be generated from MCLK
>>>>>> +      or internal PLL. In turn PLL can reference from MCLK
>>>>>> +      and BCLKs.
>>>>>>
>>>>>>       clock-names:
>>>>>> -    items:
>>>>>> -      - const: mclk
>>>>>> +    description: |
>>>>>> +      The clock names can be combination of following:
>>>>>> +        "mclk"        : Master clock
>>>>>> +        "pll_ref"     : Reference to CODEC PLL clock
>>>>>> +        "sysclk"      : CODEC SYSCLK
>>>>>> +        "^bclk[1-4]$" : Bit clocks to CODEC
>>>>> No, that does not look correct. You allow anything as clock input (even
>>>>> 20 clocks, different names, any order). That's not how DT schema should
>>>>> work and that's not how hardware looks like.
>>>>> Usually the clock inputs are always there which also you mentioned in
>>>>> description - "multiple clock inputs". All these clocks should be
>>>>> expected, unless really the wires (physical wires) can be left disconnected.
>>>> The CODEC can receive multiple clocks but all the input clocks need not
>>>> be present or connected always. If a specific configuration is needed
>>>> and platform supports such an input, then all these inputs can be added.
>>>> I don't know how to define this detail in the schema. If I make all of
>>>> them expected, then binding check throws errors. If I were to list all
>>>> the possible combinations, the list is going to be big (not sure if this
>>>> would be OK?).
>>> Thanks for explanation. Please differentiate between these two:
>>> 1. clock inputs connected, but unused (not needed for driver or for
>>> particular use case),
>>> 2. clock inputs really not connected.
>>>
>>> For the 1. above, such clock inputs should still be listed in the
>>> bindings and DTS. For the 2. above, such clocks should actually not be
>>> there.
>> Thank you for the suggestion.
>>
>>> How to achieve this depends on number of your combinations. IOW,
>>> how many clocks are physically optional.
>>   From CODEC point of view all these clock inputs are possible and a
>> platform may choose to connect a subset of it depending on the
>> application. The binding is expected to support all such cases. To
>> support all possibilities, the total combinations can be very big (100+).
>>
>>> For some small number of
>>> variations this can be:
>>> oneOf:
>>>    - const: mclk
>>>    - items:
>>>      - const: mclk
>>>      - enum:
>>>          - bclk1
>>>          - bclk2
>>>          - bclk3
>>>          - bclk4
>>>    - items:
>>>      - const: mclk
>>>      - const: pll_ref
>>>      - enum:
>>>          - bclk1
>>>          - bclk2
>>>          - bclk3
>>>          - bclk4
>>>
>>> For a total flexibility that any clock input can be disconnected, this
>>> should be a list of enums I guess (with minItems). However please find
>>> the clocks always connected and include them if possible in a fixed way
>>> (like this oneOf above).
>> May be I can list the most commonly required combinations like below and
>> extend it whenever there is a need for specific combination?
> Yes, this would work. Relaxing such constraints is possible.

Thanks. I will update this in next revision.