linux-kernel - Re: [PATCH v2 1/2] media: dt-bindings: allwinner: video-engine: Fix number of IOMMU channels

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Date:   Fri, 18 Nov 2022 09:09:01 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jernej Škrabec <jernej.skrabec@...il.com>,
        mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, wens@...e.org,
        samuel@...lland.org
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] media: dt-bindings: allwinner: video-engine: Fix
 number of IOMMU channels

On 17/11/2022 21:31, Jernej Škrabec wrote:
> Dne četrtek, 17. november 2022 ob 14:13:00 CET je Krzysztof Kozlowski 
> napisal(a):
>> On 17/11/2022 07:07, Jernej Skrabec wrote:
>>> Cedrus (video engine) on Allwinner H6 actually uses two IOMMU channel,
>>> not just one. However, Cedrus on SoCs like D1 only uses one channel.
>>>
>>> Allow up to 2 IOMMU channels.
>>>
>>> Fixes: 62a8ccf3a248 ("arm64: dts: allwinner: h6: Fix Cedrus IOMMU usage")
>>> Signed-off-by: Jernej Skrabec <jernej.skrabec@...il.com>
>>> ---
>>>
>>>  .../bindings/media/allwinner,sun4i-a10-video-engine.yaml       | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git
>>> a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engin
>>> e.yaml
>>> b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engin
>>> e.yaml index 541325f900a1..6446004d59d9 100644
>>> ---
>>> a/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engin
>>> e.yaml +++
>>> b/Documentation/devicetree/bindings/media/allwinner,sun4i-a10-video-engin
>>> e.yaml> 
>>> @@ -55,7 +55,8 @@ properties:
>>>      description: Phandle to the device SRAM
>>>    
>>>    iommus:
>>> -    maxItems: 1
>>> +    minItems: 1
>>> +    maxItems: 2
>>
>> You have several compatibles in the file, so usually this is further
>> constrained per each variant in allOf:if:then:.
> 
> Usually, yes. But this whole binding would need update. It has a few optional 
> properties and none of them is tied to any compatible. Additionally, if I do 
> it as you suggest, then Robs automatic test will report the issue, because 
> existing H6 based boards won't match this binding anymore. I would much rather 
> send follow up patch which clears up all optional properties.

I don't understand last argument. It's basically like saying - I keep
bindings not really correct, because otherwise I would see warnings and
I would need to fix them.

If this can be constrained per variant, constrain it and then fix the
boards.
Best regards,
Krzysztof