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Date:   Mon, 28 Mar 2022 18:49:17 +0530
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Subject: Re: [RFC PATCH v2 3/6] ASoC: dt-bindings: Extend clock bindings of
 rt5659
Content-Language: en-US
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
References: <1648448050-15237-1-git-send-email-spujar@nvidia.com>
 <1648448050-15237-4-git-send-email-spujar@nvidia.com>
 <da414b44-1bec-5918-84f5-9dfff2009f41@kernel.org>
 <53d77f33-27e8-3446-d758-3e545eea2db4@nvidia.com>
 <5e4e11b5-02b8-e03e-2924-c9f2882921be@kernel.org>
From:   Sameer Pujar <spujar@nvidia.com>
In-Reply-To: <5e4e11b5-02b8-e03e-2924-c9f2882921be@kernel.org>
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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?

   clock-names:
     oneOf:
       - const: mclk
       - pattern: '^bclk[1-4]$'
       - items:
           - const: mclk
           - pattern: '^bclk[1-4]$'
       - items:
           - const: mclk
           - const: sysclk
       - items:
           - const: mclk
           - const: pll_ref
           - const: sysclk
       - items:
           - pattern: '^bclk[1-4]$'
           - const: pll_ref
           - const: sysclk
       - items:
           - const: mclk
           - pattern: '^bclk[1-4]$'
           - const: pll_ref
           - const: sysclk