linux-kernel - Re: [PATCH v3 3/6] media: dt-bindings: mediatek,vcodec: Remove VDEC

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Date:   Tue, 20 Jun 2023 15:00:00 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, kernel@...labora.com,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Yunfei Dong <yunfei.dong@...iatek.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3 3/6] media: dt-bindings: mediatek,vcodec: Remove
 VDEC_SYS for mt8183

On 20/06/2023 14:46, Nícolas F. R. A. Prado wrote:
> On Tue, Jun 20, 2023 at 10:12:14AM +0200, Krzysztof Kozlowski wrote:
>> On 20/06/2023 02:03, Nícolas F. R. A. Prado wrote:
>>> The binding expects the first register space to be VDEC_SYS. But on
>>> mt8183, which uses the stateless decoders, this space is used only for
>>> controlling clocks and resets, which are better described as separate
>>> clock-controller and reset-controller nodes.
>>>
>>> In fact, in mt8173's devicetree there are already such separate
>>> clock-controller nodes, which cause duplicate addresses between the
>>> vdecsys node and the vcodec node. But for this SoC, since the stateful
>>> decoder code makes other uses of the VDEC_SYS register space, it's not
>>> straightforward to remove it.
>>>
>>> In order to avoid the same address conflict to happen on mt8183,
>>> since the only current use of the VDEC_SYS register space in
>>> the driver is to read the status of a hardware controlled clock, remove
>>> the VDEC_SYS register space from the binding and describe an extra
>>> syscon that will be used to directly check the hardware status.
>>>
>>> Also add reg-names to be able to tell that this new register schema is
>>> used, so the driver can keep backward compatibility.
>>>
>>> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>>>
>>> ---
>>> I dropped the tags from this commit since a syscon is now used instead
>>> of an extra clock.
>>>
>>> Changes in v3:
>>> - Removed the active clock
>>> - Added a mediatek,vdecsys syscon property
>>>
>>> Changes in v2:
>>> - Merged with patch 1 (media: dt-bindings: mediatek,vcodec: Allow single
>>>   clock for mt8183) to avoid changing number of clocks twice
>>> - Added maxItems to reg-names
>>> - Constrained clocks for each compatible
>>> - Reordered properties for each compatible
>>>
>>>  .../media/mediatek,vcodec-decoder.yaml        | 30 +++++++++++++++++++
>>>  1 file changed, 30 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/media/mediatek,vcodec-decoder.yaml b/Documentation/devicetree/bindings/media/mediatek,vcodec-decoder.yaml
>>> index 1e56ece44aee..2f625c50bbfe 100644
>>> --- a/Documentation/devicetree/bindings/media/mediatek,vcodec-decoder.yaml
>>> +++ b/Documentation/devicetree/bindings/media/mediatek,vcodec-decoder.yaml
>>> @@ -21,8 +21,13 @@ properties:
>>>        - mediatek,mt8183-vcodec-dec
>>>  
>>>    reg:
>>> +    minItems: 11
>>>      maxItems: 12
>>>  
>>> +  reg-names:
>>> +    minItems: 11
>>> +    maxItems: 11
>>
>> maxItems: 12
>>
>>> +
>>>    interrupts:
>>>      maxItems: 1
>>>  
>>> @@ -60,6 +65,10 @@ properties:
>>>      description:
>>>        Describes point to scp.
>>>  
>>> +  mediatek,vdecsys:
>>> +    $ref: /schemas/types.yaml#/definitions/phandle
>>> +    description: Phandle to the vdecsys syscon node.
>>> +
>>>  required:
>>>    - compatible
>>>    - reg
>>> @@ -79,8 +88,26 @@ allOf:
>>>      then:
>>>        required:
>>>          - mediatek,scp
>>> +        - mediatek,vdecsys
>>>  
>>>        properties:
>>> +        reg:
>>> +          maxItems: 11
>>> +
>>> +        reg-names:
>>> +          items:
>>> +            - const: misc
>>> +            - const: ld
>>> +            - const: top
>>> +            - const: cm
>>> +            - const: ad
>>> +            - const: av
>>> +            - const: pp
>>> +            - const: hwd
>>> +            - const: hwq
>>> +            - const: hwb
>>> +            - const: hwg
>>> +
>>>          clocks:
>>>            minItems: 1
>>>            maxItems: 1
>>> @@ -101,6 +128,9 @@ allOf:
>>>          - mediatek,vpu
>>>  
>>>        properties:
>>> +        reg:
>>> +          minItems: 12
>>
>>
>> What about reg-names here? They should be also defined and in sync with
>> regs.
> 
> That's intentional. As described in the commit message, mt8173 will keep having
> the VDEC_SYS iospace, while mt8183 won't. And we use the presence of reg-names
> to tell them apart.
> 
> So, mt8173 has 12 regs, no reg-names and no syscon, while mt8183 has 11 regs,
> with reg-names and the syscon.

reg-names is not the way to tell apart variants. Compatible is. If you
add reg-names for one variant, it's expected to have it defined for
other as well, because the order of items in reg is always fixed.

Best regards,
Krzysztof