Re: [PATCH 1/2] media: iris: Fix iova allocation from restrict region

[Dmitry Baryshkov]

On Wed, Aug 12, 2026 at 04:25:58PM +0530, Vishnu Reddy 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
> 
> A series to reserve the 0-600MB IOVA range via "iommu-addresses" was
> already posted here:
> https://lore.kernel.org/all/20260807-iris_iova_600mb_fix-v1-0-3996f67e33f9@xxxxxxxxxxxxxxxx
> 
> Those changes involve DT binding and DT node changes, and discussion is
> still ongoing on how to handle those for stable and for the upcoming
> sub-node design, with no conclusion reached yet. Thereby a critical reset
> issue is still open.
> 
> This is an alternate solution to fix the unhandled SMMU page fault
> by restricting the IOVA range in the video driver, which also makes it
> easier and faster to land on mainline and stable kernels. At the same
> time the patch only reserves in the IOVA space without allocating
> any physical memory.
> 
> Currently sub-nodes are not yet present, and only a single device is
> available, so the restriction is applied to both non-pixel and pixel
> stream IDs. This makes the solution unoptimal while fixing the issue
> considering all scenarios.
> Once sub-nodes for non-pixel, pixel, and secure streams become available,
> the restriction can be made stream specific.
> 
> Fixes: d7378f84e94e ("media: iris: introduce iris core state management with shared queues")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
> ---
>  drivers/media/platform/qcom/iris/iris_core.h  |  6 +++
>  drivers/media/platform/qcom/iris/iris_probe.c | 69 ++++++++++++++++++++++++++-
>  2 files changed, 74 insertions(+), 1 deletion(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>


-- 
With best wishes
Dmitry