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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 6/8/26 4:37 PM, 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

Mainly or exclusively?

Konrad

> 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@oss.qualcomm.com>
>>> ---
>>>   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
>>>
>>
> 
>