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

On 8/7/2026 9:54 PM, Rob Herring wrote:
> On Fri, Aug 07, 2026 at 12:03:50PM +0300, Dmitry Baryshkov wrote:
>> On Fri, Aug 07, 2026 at 01:54:48PM +0530, Vikash Garodia wrote:
>>> From: Daniel J Blueman <[email protected]>
>>>
>>> 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: [email protected]
>>> Signed-off-by: Daniel J Blueman <[email protected]>
>>> Signed-off-by: Vikash Garodia <[email protected]>
>>> ---
>>>  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.
> I think this is an abuse of /reserved-memory. reserved-memory is 
> reserved *physical* memory. Reserved IOVA is a property on top of that. 
> I'm surprised this passes validation. If it does, I may go fix that.

As per the reserved-memory.yaml schema document, the iommu-addresses
property for IOVA reservation into /reserved-memory is allowed — it's
documented for IOVA carveout reservations:
https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/reserved-memory/reserved-memory.yaml#L56

> Rob
>