Re: [PATCH v2 04/12] media: iris: Add helper to create a context bank device

[Krzysztof Kozlowski]

On 06/08/2026 12:08, Vikash Garodia wrote:
> 
> 
> On 8/6/2026 2:27 PM, Dmitry Baryshkov wrote:
>> On Fri, Jul 31, 2026 at 11:52:19PM +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. A stream can only be confined to its range if it
>>> has an IOMMU domain of its own, and the IOMMU core attaches a domain per
>>> struct device, so each stream needs its own device.
>>> Add iris_create_cb_dev(), which looks up a named child of the iris node
>>> and registers it as a platform device parented to the iris core. The
>>> child's fwnode is handed to platform_device_register_full() so the OF
>>> core applies that subnode's "iommus" property and the new device gets
>>> its own IOMMU domain. The DMA mask comes from platform data, and the
>>> segment size and boundary are capped at 32 bits to match the addressing
>>> the VPU performs.
>>> Return NULL when the named child is absent, so callers can treat a
>>> device tree without context bank subnodes as a supported configuration
>>> rather than an error.
>>> Backports are intended since the first DTS of 8550 binding schema.
>>
>> What does this mean in the commit message?
>>
>>>
>>> Fixes: 41661853ae8e ("arm64: dts: qcom: sm8550: add iris DT node")
>>
>> How can driver fix the DT?
>>
> 
> The idea is to backport the driver fixes till the kernels when the first 
> DTS landed. Ideally the fixes tags the commit which introduced the bug, 
> while in this case, was thinking to keep it for DTS.

Fixes tag does not represent the backport, so your idea is wrong. You
point here to the commit which introduced incorrect code.

If DTS is incorrect, then a DTS patch fixes it. How a driver can fix
DRIVER-INDEPENDENT hardware description? It's contradictory to the
"independent" part.

Best regards,
Krzysztof