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

On 8/10/2026 7:17 PM, Rob Herring wrote:
> On Sat, Aug 8, 2026 at 4:55 AM Bryan O'Donoghue <[email protected]> wrote:
>>
>> On 08/08/2026 05:37, Vishnu Reddy wrote:
>>>
>>> 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
>> I think that is an entirely reasonable reading of the text
>>
>> Quote:
>>
>> "If no "reg" property is specified, the "iommu-addresses" property
>>    defines carveout regions in the IOVA space for the given device. This
>>    can be useful if a certain memory region should not be mapped through
>>    the IOMMU."
>>
>> Which is exactly what this series does. Excludes a specific IOVA range
>> from being allocated for this device.
> 
> But if "iommu-addresses" is the only property of the reserved memory,
> why put this property in reserved-memory rather than directly in the
> device's node? I'm only questioning where is the right place to
> describe a reserved IOVA.
> 

a single property node vs multi-property node should not be the reason 
to decide the place i believe, rather having them all under 
reserve-memory keeps all reservation at one place instead of scattering 
it all over.

Regards,
Vikash

> Rob