Re: [PATCH 04/22] arm64: dts: qcom: hamoa: Reserve low IOVA range for Iris

[Dmitry Baryshkov]

On Fri, Aug 07, 2026 at 01:54:48PM +0530, Vikash Garodia wrote:
> From: Daniel J Blueman <daniel@xxxxxxxxx>
> 
> On X1-family hamoa platforms, the Iris VPU reserves IOVA addresses
> below 0x25800000 (600MB), primarily for secure non-pixel buffers. DMA
> into that range, from any other stream id would triggers unhandled SMMU
> page faults that cause spontaneous device reboots. This is readily
> reproduced with one or more browser tabs driving multiple concurrent
> video decode streams.
> 
> Add a reserved-memory IOVA reservation node covering [0, 0x25800000]
> and reference it from the Iris node so the IOMMU layer keeps DMA
> allocations above that boundary.
> 
> Link: https://github.com/qualcomm-linux/kernel-topics/issues/1157#issuecomment-4458933574
> Fixes: 9065340ac04d ("arm64: dts: qcom: x1e80100: Add IRIS video codec")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Daniel J Blueman <daniel@xxxxxxxxx>
> Signed-off-by: Vikash Garodia <vikash.garodia@xxxxxxxxxxxxxxxx>
> ---
>  arch/arm64/boot/dts/qcom/hamoa.dtsi | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/hamoa.dtsi b/arch/arm64/boot/dts/qcom/hamoa.dtsi
> index 8a96ea1bdb9c4c409b2af997680d8c13fed0643e..87f424765d513c97b06303bceb75ca9f176d2ace 100644
> --- a/arch/arm64/boot/dts/qcom/hamoa.dtsi
> +++ b/arch/arm64/boot/dts/qcom/hamoa.dtsi
> @@ -666,6 +666,17 @@ smem_mem: smem@ffe00000 {
>  			hwlocks = <&tcsr_mutex 3>;
>  			no-map;
>  		};
> +
> +		/*
> +		 * The Iris VPU reserves IOVA below 0x25800000 (600MB),
> +		 * primarily for non-pixel buffers using different Stream IDs.
> +		 * DMA into that range triggers unhandled SMMU faults and
> +		 * spontaneous reboots, so reserve it to keep IOMMU
> +		 * allocations above this boundary.
> +		 */
> +		iris_iova: iris-iova {
> +			iommu-addresses = <&iris 0x0 0x0 0x0 0x25800000>;
> +		};
>  	};
>  
>  	qup_opp_table_100mhz: opp-table-qup100mhz {
> @@ -5439,7 +5450,7 @@ &config_noc SLAVE_VENUS_CFG QCOM_ICC_TAG_ACTIVE_ONLY>,
>  			interconnect-names = "cpu-cfg",
>  					     "video-mem";
>  
> -			memory-region = <&video_mem>;
> +			memory-region = <&video_mem>, <&iris_iova>;

I don't like the idea of this series, because it _again_ doesn't tell us
the truth about the hardware. This typicall ends up with bigger problems
later on, when it starts to affect other bits and pieces.

I don't want to NAK it, but I'd strongly ask to reconsider it.

>  
>  			resets = <&gcc GCC_VIDEO_AXI0_CLK_ARES>;
>  			reset-names = "bus";
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry