Re: [PATCH v2 01/12] dt-bindings: media: qcom,venus: Add context bank subnodes to common schema

[Vikash Garodia <vikash.garodia@oss.qualcomm.com>]

On 8/6/2026 2:19 PM, Dmitry Baryshkov wrote:
> On Fri, Jul 31, 2026 at 11:52:16PM +0530, Vikash Garodia wrote:
>> The VPU issues DMA through several SMMU streams, and the hardware does
>> not give every stream the same addressable range. The non-pixel stream
>> is restricted to use 0-600MB of IOVA space, while the pixel stream can
>> address the full range:
>>      +-----------------------------------------------------------+
>>      | non-pixel stream addressable range (600 MB - 3.5 GB)      |
>>      | 0x25800000 - 0xe0000000                                   |
>>      +-----------------------------------------------------------+
>>      | pixel stream addressable range (0 - 3.5 GB)               |
>>      | 0x00000000 - 0xe0000000                                   |
>>      +-----------------------------------------------------------+
>> A single "iommus" property on the video-codec node puts every stream in
>> one IOMMU domain sharing one IOVA allocator, so nothing keeps a
>> non-pixel buffer inside the low 600 MB. Once an allocation lands below
>> that boundary the hardware faults, which shows up as unhandled SMMU page
>> faults and spontaneous reboots:
>> https://gitlab.freedesktop.org/drm/msm/-/work_items/100
>>
>>   
>> +  dma-ranges: true
>> +
>> +  '#address-cells':
>> +    const: 2
>> +
>> +  '#size-cells':
>> +    const: 2
> 
> This would conflict with the 32-bit addressed Venus nodes (and it will
> also break examples). So both should be just 'true'

With "true", i see following comment from sashiko (when ran locally)

Without a const constraint, a device tree could specify #address-cells = 
<1> or a non-empty dma-ranges, and it would silently pass schema 
validation. The DT bindings guidelines also recommend that cell-count 
properties have a const constraint matching the hardware.

> 
>>   
>> +oneOf:
>> +  - required:
>> +      - iommus
>> +  - required:
>> +      - non-pixel
>> +      - pixel
> 
> - #address-cells
> - #size-cells
> - dma-ranges
> 
>> +
>>   additionalProperties: true
>>
>> -- 
>> 2.34.1
>>
>