linux-kernel - Re: [PATCH v2 1/8] media: dt-bindings: qcom-kaanapali-iris: Add kaanapali video codec binding

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Message-ID: <24719933-d81f-41cb-aabc-e28f018b156c@kernel.org>
Date: Wed, 22 Oct 2025 18:28:29 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Vikash Garodia <vikash.garodia@....qualcomm.com>,
 Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>,
 Abhinav Kumar <abhinav.kumar@...ux.dev>, Bryan O'Donoghue <bod@...nel.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>,
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: linux-arm-msm@...r.kernel.org, linux-media@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Vishnu Reddy <quic_bvisredd@...cinc.com>
Subject: Re: [PATCH v2 1/8] media: dt-bindings: qcom-kaanapali-iris: Add
 kaanapali video codec binding

On 22/10/2025 17:36, Konrad Dybcio wrote:
>>
>> [    1.361157] pc : qcom_smmu_write_s2cr+0x64/0xa4
>> [    1.361165] lr : arm_smmu_write_s2cr+0x2c/0xbc
>> [    1.361168] sp : ffff80008005b8f0
>> [    1.361169] x29: ffff80008005b8f0 x28: 0000000000000000 x27: ffffc7f252f45320
>> ....
>> [    1.361195] x2 : ffff800081200c48 x1 : 0000000000000048 x0 : ffff800081200000
>> [    1.361198] Call trace:
>> [    1.361199]  qcom_smmu_write_s2cr+0x64/0xa4 (P)
>> [    1.361203]  arm_smmu_master_install_s2crs+0x7c/0xac
>> [    1.361207]  arm_smmu_attach_dev+0xb0/0x1d4
>>
>> Could you please suggest on listing the iommu items ? I did not find the
>> relevant references in other bindings where flexible iommus is being listed.
> 
> Krzysztof would probably like to see what I believe someone else somewhere
> sometime suggested in the iommus discussions (sorry it's not possible to
> keep track of it all), where the DT can list every possible required iommu
> sid, but the driver ensures only the ones that are necessary are utilized.
> 
> This will require big changes to the iommu framework though, I'm afraid
> 
>>> I already asked this.
>>>
>>>> +
>>>> +  memory-region:
>>>> +    minItems: 1
>>>> +    maxItems: 2
>>>
>>> Same comment. I already asked this about iommus.
>>
>> Same here, there aren't any bindings which lists for flexible memory-region.
>> Please suggest if there are any such references.
> 
> Similarly, we can define the additional memory region that's necessary
> for $reasons and leave it unused in the driver (actually I don't know
> why there may be two, but let's assume it's a QTEE/noQTEE detail), because
> for the hw to operate, it must be set up by some entity in the system
> either way (i.e. the memory is reserved even if it's not done by Linux)


Another point is pretty obvious: if one claims that
iommus/memory-regions list is flexible - some elements are optional -
then clearly there is a distinction which elements are mandatory and
which are optional. So there is difference between elements of the
array. If there is a difference, they all must be explicitly listed,
like every other list (clocks, resets etc) property. Writing bindings
doc also defines this rule.

Best regards,
Krzysztof