Re: [PATCH v3 02/13] dt-bindings: media: qcom,sm8550-iris: Add context bank subnodes
From: Dmitry Baryshkov
Date: Wed Sep 09 2026 - 17:08:08 EST
On Wed, Sep 09, 2026 at 08:27:09PM +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@xxxxxxxxxx
>
> 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@xxxxxxxxxx/
>
> Update example to the subnode form. Doing so, it picks up the supporting
> properties needed on the video-codec node, address-cells, size-cells and
> dma-ranges to declare 1:1 DMA translation into the parent. Given a soc
> with address-cells and size-cells as 2, update the video-codec "reg"
> accordingly.
>
> This patch depends-on:
> https://github.com/devicetree-org/dt-schema/pull/207
>
> Tested-by: Daniel J Blueman <daniel@xxxxxxxxx>
> Co-developed-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vikash Garodia <vikash.garodia@xxxxxxxxxxxxxxxx>
> ---
> .../bindings/media/qcom,sm8550-iris.yaml | 118 ++++++++++++---------
> 1 file changed, 67 insertions(+), 51 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> index 0400ca1bff05dcef6b742c3fbf77e38adca9f280..dd80526838f1193f4c9105793ae4bf4fe0755ec2 100644
> --- a/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> +++ b/Documentation/devicetree/bindings/media/qcom,sm8550-iris.yaml
> @@ -98,10 +98,10 @@ required:
> - interconnect-names
> - resets
> - reset-names
> - - iommus
> - dma-coherent
>
> allOf:
> + - $ref: qcom,venus-common.yaml#
> - if:
> properties:
> compatible:
> @@ -150,70 +150,86 @@ examples:
> #include <dt-bindings/power/qcom-rpmpd.h>
> #include <dt-bindings/power/qcom,rpmhpd.h>
>
> - video-codec@aa00000 {
> - compatible = "qcom,sm8550-iris";
> - reg = <0x0aa00000 0xf0000>;
> - interrupts = <GIC_SPI 174 IRQ_TYPE_LEVEL_HIGH>;
> + soc {
> + #address-cells = <2>;
> + #size-cells = <2>;
No. The SoC node must go away. None of the schema examples have it.
>
> - power-domains = <&videocc VIDEO_CC_MVS0C_GDSC>,
> - <&videocc VIDEO_CC_MVS0_GDSC>,
> - <&rpmhpd RPMHPD_MXC>,
> - <&rpmhpd RPMHPD_MMCX>;
--
With best wishes
Dmitry