Re: [PATCH v3 3/6] arm64: dts: qcom: kodiak: Add GEM_NOC interconnect for adreno SMMU

[Val Packett <val@packett.cool>]

Hi,

On 7/17/26 8:40 AM, Bibek Kumar Patro wrote:
>
>
> On 7/8/2026 8:56 PM, Bjorn Andersson wrote:
>> On Wed, Jul 08, 2026 at 03:31:07PM +0530, Bibek Kumar Patro wrote:
>>>
>>>
>>> On 7/7/2026 10:14 PM, Dmitry Baryshkov wrote:
>>>> On Tue, Jul 07, 2026 at 06:37:24PM +0530, Bibek Kumar Patro wrote:
>>>>>
>>>>>
>>>>> On 7/6/2026 11:12 PM, Dmitry Baryshkov wrote:
>>>>>> On Mon, Jul 06, 2026 at 10:26:36PM +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.
>>>>>>>
>>>>>>> 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 90e50c245c0c..721526f023dd 100644
>>>>>>> --- a/arch/arm64/boot/dts/qcom/kodiak.dtsi
>>>>>>> +++ b/arch/arm64/boot/dts/qcom/kodiak.dtsi
>>>>>>> @@ -3389,6 +3389,8 @@ 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>;
>>>>>>
>>>>>> Why is it ALWAYS? Would it be better to declare it as ACTIVE_ONLY 
>>>>>> and
>>>>>
>>>>> Added QCOM_ICC_TAG_ALWAYS, to hold the vote in SLEEP bucket as well
>>>>> preventing gem_noc going to sleep when icc_set_bw is being called.
>>>>
>>>> _why_?
>>>>
>>>
>>> Now when i think of where we implemented the hooks, ALWAYS is not 
>>> needed. We
>>> should keep it ACTIVE_ONLY since we are already voting it
>>> back in resume pah. I'll fix it in next revision.
>>>
>>
>> The path is between the SMMU and DDR, so clearly it has to do with the
>> TCU's ability to fetch things from DDR.
>>
>
> Yes as you rightly mentioned, this series is helping to resolve the 
> race in TCU DDR clink
>
>> ACTIVE_ONLY states that the vote should only be applied when the
>> application subsystem (CPUSS) is not in low-power mode (CPU is active).
>>
>> So, are you saying that in all cases that cpuidle might select such
>> low-power state the GPU TCU is "stopped", and does not need to perform
>> any memory transactions?
>>
>
> I rechecked the architectural block diagram, GPU TCU is
> independent of the CPUSS, unlike system TCU.
>
> This means CPUSS can be powered down while the GPU TCU remains voted 
> up. While this series was intended to avoid a DDR voting race between the
> GPU TCU and its clients, using ACTIVE_ONLY could have possibly
> introduced a race between CPUSS and the GPU TCU itself.
>
> Thanks for catching this in my reply Bjorn.
>
> ACTIVE_ONLY would have been suitable for system TCU (apps_smmu)
> for which the interconnect field is anyways not needed, but
> unsuitable for GPU TCU.
>
>>
>> To me these two are orthogonal and TAG_ALWAYS is logically correct, but
>> perhaps there's some practical dependency that I'm missing?
>>
>
> We can ignore my acknowledgment [1] on previous response, Dmitry.
> ALWAYS TAG is correct here instead of ACTIVE_ONLY in the interconnect 
> field for adreno SMMU. 


This series seems to help with a really annoying bug on Kodiak phones 
like sm7325-motorola-dubai where often boot would hang when initializing 
the display panel (so it took a few reboots to successfully boot the 
device).

And indeed it only helps with the ALWAYS tag..

I've had this patch applied for a while (without even realizing that it 
fixed that!! thought the issue was gone because of something else) and 
today I went around kodiak.dtsi trying to remove unnecessary ALWAYS 
votes… first boot after changing this tag to ACTIVE_ONLY and boom, hang.


Tested-by: Val Packett <val@packett.cool> # sm7325-motorola-dubai

(for patch 2 i.e. the driver code as well)


Thanks,
~val