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

[Rob Herring <robh@kernel.org>]

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.

Rob