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

On 8/12/2026 4:25 PM, 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- 
> [email protected]
> 
> 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: af2c3834c8ca ("[media] media: venus: adding core part and helper functions")
> Cc:[email protected]
> Signed-off-by: Vishnu Reddy<[email protected]>
> ---
>   drivers/media/platform/qcom/venus/core.c | 71 +++++++++++++++++++++++++++++++-
>   drivers/media/platform/qcom/venus/core.h |  5 +++
>   2 files changed, 74 insertions(+), 2 deletions(-)


Reviewed-by: Vikash Garodia <[email protected]>