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

[Bryan O'Donoghue <bod@kernel.org>]

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 <daniel@quora.org>
>>>>
>>>> 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@vger.kernel.org
>>>> Signed-off-by: Daniel J Blueman <daniel@quora.org>
>>>> Signed-off-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
>>>> ---
>>>>   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.

---
bod