Re: [PATCH v3 01/13] dt-bindings: media: qcom,venus: Add context bank subnodes to common schema

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

On 9/10/2026 12:29 PM, Krzysztof Kozlowski wrote:
> On Wed, Sep 09, 2026 at 08:27:08PM +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
>> cannot address the low 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 restricts a
>> non-pixel buffer to avoid 0 to 600MB. 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
>>
>> Given that the address range restriction is for specific VPU stream, it
>> should be ideally be moved to that stream. To achieve the same, a subset
>> of streams is now represented as subnodes, so that each can be
>> associated with its respective addressable range. The design was
>> discussed and agreed by mainatiners here
>> https://lore.kernel.org/all/c7b956a9-d3e8-4e18-b780-5d08f5cd2ca1@kernel.org
>>
>> In the past, this limitation was addressed with an iommu-map approach,
>> with the iris driver dynamically creating the devices. That approach was
>> later concluded to be a hack to avoid having subnodes, and was NAKed by
>> the iommu maintainers. It was discussed in detail here:
>> https://lore.kernel.org/all/c7b956a9-d3e8-4e18-b780-5d08f5cd2ca1@kernel.org/
>>
>> "iommu-ranges" on the subnode describes the *allowed* IOVA range that
>> stream is allowed to use, so the IOVA is allocated from the specified
>> range only. Define all the possible subnodes so as to describe all the
>> VPU hardware iommu interfaces, both secure as well as non secure.
>>
>> address-cells, size-cells and dma-ranges declares the 1:1 DMA
>> translation into the parent.
>>
>> The parent "iommus" is kept as an alternative via "oneOf", so platforms
>> that have not been converted to subnodes still validate. New platforms
>> should use the subnode form.
>>
>> This patch depends-on:
>> https://github.com/devicetree-org/dt-schema/pull/207
> 
> Please drop, not suitable for commit, keep it in the changelog
> 

Sure, will add this to changelog.

>>
>>   Tested-by: Daniel J Blueman <daniel@quora.org>
> 
> Plese drop, not true here
> 

ok, got picked in b4 trailers, will drop.

> 
>> Signed-off-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
>> ---
>>   .../bindings/media/qcom,sc7180-venus.yaml          | 15 ----
>>   .../bindings/media/qcom,venus-common.yaml          | 97 ++++++++++++++++++++++
>>   2 files changed, 97 insertions(+), 15 deletions(-)
>>
> 
> I see this causes DT checks failures but I don't see the report, so
> probably it was because of schema dependency.
> 
> Best regards,
> Krzysztof