Re: [PATCH v2 3/6] arm64: dts: qcom: kodiak: Add GEM_NOC interconnect for adreno SMMU

[Bibek Kumar Patro]

On 6/8/2026 7:27 PM, Dmitry Baryshkov wrote:
> On Tue, May 26, 2026 at 08:12:04PM +0530, Bibek Kumar Patro wrote:
> > On Kodiak platforms, the Adreno SMMU requires a bandwidth vote on
> > the GEM_NOC path (MASTER_GPU_TCU -> SLAVE_EBI1) before its registers
> > are accessible. Without this vote, the SMMU may become unreachable,
> > leading to intermittent probe failures and runtime issues.
> >
> > Add the required interconnect to ensure reliable register access.
>
> Does it only concern the GPU SMMU? What about the APPS SMMU? Should it
> be voting on other interconnects too? I guess so, because currently I
> see that TBUs vote for various interconnects. BTW: should apps_smmu also
> vote on the power domains?

This race mainly occurs in GPU SMMU, where the GDSC can have an
independent vote on the Adreno SMMU. However, the GEM_NOC vote may
already have been removed by the GPU (or any consumer of adreno_smmu,
e.g gmu), unless it is explicitly voted by the GPU SMMU (which acts as a
supplier for the GPU). This mismatch can lead to SHUB timeouts or NoC
errors.

Mostly this race reported in suspend/resume cycle (when gpu/gmu devices 
moves to slumber/suspend state before adreno_smmu powers down
and the later doesn't have explicit interconnect voting).

In the case of APPS SMMU, such a race is not expected for any known
use case. APPS SMMU is part of a shared infrastructure block, and its
power is typically kept enabled as long as attached master devices are
active. Therefore, explicit power-domain voting from APPS SMMU may not
be required.

Thanks,
Bibek


> > Signed-off-by: Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/boot/dts/qcom/kodiak.dtsi | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/kodiak.dtsi b/arch/arm64/boot/dts/qcom/kodiak.dtsi
> > index fa540d8c2615dc02d941eb16bc7253204c2750bd..eefa4b836a81374ff437ab4bbcbc3fecc1590ab6 100644
> > --- a/arch/arm64/boot/dts/qcom/kodiak.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/kodiak.dtsi
> > @@ -3386,6 +3386,8 @@ adreno_smmu: iommu@3da0000 {
> >   
> >   			power-domains = <&gpucc GPU_CC_CX_GDSC>;
> >   			dma-coherent;
> > +			interconnects = <&gem_noc MASTER_GPU_TCU QCOM_ICC_TAG_ALWAYS
> > +					 &mc_virt SLAVE_EBI1 QCOM_ICC_TAG_ALWAYS>;
> >   		};
> >   
> >   		gfx_0_tbu: tbu@3dd9000 {
> >
> > --
> > 2.34.1