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

[Dmitry Baryshkov]

On Mon, Jun 08, 2026 at 08:07:07PM +0530, Bibek Kumar Patro wrote:
> 
> 
> 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.

This looks like a good part of the commit message. Please add it where
it belongs.

> 
> 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
> > > 
> > 
> 

-- 
With best wishes
Dmitry