linux-kernel - Re: [PATCH v2 1/3] dt-bindings: display: msm: qcm2290-mdss: Fix iommus property

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Message-ID: <6020af2a-5baa-4594-8cbc-bf7241f0128e@kernel.org>
Date: Fri, 16 Jan 2026 14:15:02 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Sumit Garg <sumit.garg@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 andersson@...nel.org, konradybcio@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, akhilpo@....qualcomm.com,
 vikash.garodia@....qualcomm.com, dikshita.agarwal@....qualcomm.com,
 robin.clark@....qualcomm.com, lumag@...nel.org,
 loic.poulain@....qualcomm.com, jorge.ramirez@....qualcomm.com,
 linux-kernel@...r.kernel.org, Sumit Garg <sumit.garg@....qualcomm.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: display: msm: qcm2290-mdss: Fix
 iommus property

On 16/01/2026 13:53, Sumit Garg wrote:
> On Fri, Jan 16, 2026 at 09:46:54AM +0100, Krzysztof Kozlowski wrote:
>> On Fri, Jan 16, 2026 at 11:50:02AM +0530, Sumit Garg wrote:
>>> From: Sumit Garg <sumit.garg@....qualcomm.com>
>>>
>>> Fix IOMMU DT propety for display via dropping SMMU stream IDs which
>>> relates to secure context bank. Assigning Linux kernel (HLOS) VMID
>>> to secure context bank stream IDs is incorrect.
>>>
>>> The min value is added for iommus property to ensure in future when
>>> secure context bank stream IDs are properly supported then the iommus
>>> property is extensible.
>>>
>>> These DT bindings changes should be backwards compatible.
>>>
>>> Signed-off-by: Sumit Garg <sumit.garg@....qualcomm.com>
>>> ---
>>>  .../devicetree/bindings/display/msm/qcom,qcm2290-mdss.yaml   | 5 ++---
>>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/display/msm/qcom,qcm2290-mdss.yaml b/Documentation/devicetree/bindings/display/msm/qcom,qcm2290-mdss.yaml
>>> index f0cdb5422688..5c888f07bc0b 100644
>>> --- a/Documentation/devicetree/bindings/display/msm/qcom,qcm2290-mdss.yaml
>>> +++ b/Documentation/devicetree/bindings/display/msm/qcom,qcm2290-mdss.yaml
>>> @@ -33,6 +33,7 @@ properties:
>>>        - const: core
>>>  
>>>    iommus:
>>> +    minItems: 1
>>
>> Same comment as other changes like that, which I already gave guideline
>> - you need to list the items (minItems stay), because you now claim the
>> order matters and is strictly defined.
> 
> Not sure if I claimed that order matters now but rather the secure bank
> stream IDs were incorrectly represented earlier in the DT.

The code claims this by saying that one specific entry is allowed, so
that entry is somehow distinctive, special, different than the other entry.

> 
> There has been ongoing disscusion related to how stream ID associated
> with different translation context can be represented in DT here [1].
> With that only the secure bank stream IDs can be properly represented.
> 
> Here I just followed the approach taken by Adreno GPU bindings for the
> iommus property [2].
> 
> [2] Documentation/devicetree/bindings/display/msm/gpu.yaml +82

Such justifications are pointless. What about commit msg which explains
why this was added? What about entire public discussion happening with
this patch? What about all previous revisions of that patch and
discussions leading to this piece of code? So you just found few lines
of code, ignored entire background and any other arguments, and copied
it here.

That's the approach - I found a piece of some buggy code, so I can do
the same.

Again, we discussed it 2-3 months ago for the same patch and I gave
exactly same reason why this patch is incomplete.


Best regards,
Krzysztof