Re: [RFC PATCH 09/11] arm64: dts: qcom: lemans: Move Iris IOMMUs to child nodes

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Using `iommu-addresses` in a `reserved-memory` node explicitly blacklists the 0-600 MB IOVA range instead of limiting the device to it.
--

--- Patch [9]: [RFC PATCH 09/11] arm64: dts: qcom: lemans: Move Iris IOMMUs to child nodes ---
commit b935406806a9ce7b7ad2277e27ed775abba4a09e
Author: Vikash Garodia <vikash.garodia@oss.qualcomm.com>

arm64: dts: qcom: lemans: Move Iris IOMMUs to child nodes

This commit splits the Iris VPU into non-pixel and pixel child nodes with
their respective IOMMUs. It attempts to restrict the non-pixel stream to
the 0-600 MB IOVA range by adding a reserved IOVA range.

> diff --git a/arch/arm64/boot/dts/qcom/lemans.dtsi b/arch/arm64/boot/dts/qcom/lemans.dtsi
> --- a/arch/arm64/boot/dts/qcom/lemans.dtsi
> +++ b/arch/arm64/boot/dts/qcom/lemans.dtsi
> @@ -879,6 +879,10 @@ cpucp_fw_mem: cpucp-fw@db200000 {
>  			reg = <0x0 0xdb200000 0x0 0x100000>;
>  			no-map;
>  		};
> +
> +		iris_resv: reservation-iris {
> +			iommu-addresses = <&iris_non_pixel 0x0 0x0 0x0 0x25800000>;
> +		};
>  	};
>  
>  	smp2p-adsp {

[ ... ]

>  			status = "disabled";
>  
> +			iris_non_pixel: non-pixel {
> +				iommus = <&apps_smmu 0x0880 0x0400>;
> +				memory-region = <&iris_resv>;
> +			};

[Severity: High]
Will this inadvertently exclude the 0-600 MB IOVA range from the available
allocator space instead of restricting the device to it?

During domain initialization, the IOMMU subsystem parses iommu-addresses
without a reg property as an IOMMU_RESV_RESERVED region.

It then calls reserve_iova() to remove this exact range from the IOVA
allocator's available space. Because the non-pixel device is linked to this
memory-region, all subsequent DMA allocations for the non-pixel stream will
avoid the 0-600 MB range entirely.

This forces the device to use DMA allocations strictly > 600 MB, which
seems to guarantee the exact out-of-range memory accesses and device crashes
the patch intends to fix.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260709-vpu_iommu_iova_handling-v1-0-72bb62cb2dfd@oss.qualcomm.com?part=9