Re: [PATCH v3 1/6] dt-bindings: iommu: arm,smmu: Document interconnects property

[Bibek Kumar Patro]

On 7/8/2026 8:48 PM, Bjorn Andersson wrote:
> On Wed, Jul 08, 2026 at 08:22:00PM +0530, Bibek Kumar Patro wrote:
> > On 7/7/2026 10:12 PM, Dmitry Baryshkov wrote:
> > > On Tue, Jul 07, 2026 at 06:06:59PM +0530, Bibek Kumar Patro wrote:
> > > > On 7/6/2026 11:09 PM, Dmitry Baryshkov wrote:
> > > > > On Mon, Jul 06, 2026 at 10:26:34PM +0530, Bibek Kumar Patro wrote:
> > > > > > Some SoC implementations require a bandwidth vote on an interconnect
> > > > > > path before the SMMU register space is accessible. Add the optional
> > > > >
> > > > > Why is it limited only to those SoCs? Is it also applicable to other
> > > > > Qualcomm SoCs?
> > > >
> > > > I was hoping to keep this series focused on the core infrastructure
> > > > changes: the bindings, base ICC bandwidth-voting support, and DT
> > > > interconnect properties for the platforms currently supported on
> > > > Qualcomm Linux and have been validated so far.
> > > >
> > > > The additional targets have not been tested yet, so I'd prefer
> > > > to add their support in a separate follow-up series once validation
> > > > is complete, rather than growing this series further. WDYT?
> > >
> > > Then it should be a part of the commit message. All SoCs since SDM12345
> > > need to vote on the interconnect (and then, in the cover letter mention
> > > that you convert only a few of the SoCs). We possibly can help with
> > > testing on other platforms.
> >
> > Ack, sounds reasonable.
> > I'll add the first platform onwards which interconnect voting is required in
> > commit description.
>
> But to what degree is this related to a specific set of platforms? If we
> look ahead, aren't we expecting the list to grow to include all
> platforms in the end - resulting in a lot of noise and churn.

We have seen this issue consistently on SM8750 and later platforms, 
along with at least one customer-reported instance on SM8550. As a 
result, downstream Android implementations already vote for the required 
interconnect bandwidth explicitly on these platforms.

On Qualcomm Linux targets, we have observed similar issues on Kodiak, 
with a few occurrences on Talos as well.

My understanding is that the interconnects property remains optional, 
but in practice it is needed for Adreno SMMU operation on these platforms.

> Can you give an example of a platform where there is no interconnect
> path to vote for here or where it would be harmful to do so?

I do not anticipate any functional issues or side effects from
explicitly voting for the interconnect on Qualcomm platforms where the 
path exists.


> > And update the cover letter to clarify that this series adds
> > support for the Qualcomm Linux-supported targets available today, and
> > the list will be expanded in follow-up series as additional platforms
> > are enabled.
>
> The binding should not reflect what has been implemented and verified in
> Linux, it defines the contract between DeviceTree and the OS.

Since the property is optional, would it be necessary to add in AllOf
the list of compatible for which the property hasn't been added yet, or 
for the compatibles where it is added?

Thanks & regards,
Bibek

> Regards,
> Bjorn
>
> > Thanks & regards,
> > Bibek
> >
> > > > > > 'interconnects' property to the binding to allow platform DT nodes
> > > > > > to describe this path.
> > > > > >
> > > > > > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>
> > > > > > Signed-off-by: Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>
> > > > > > ---
> > > > > >     .../devicetree/bindings/iommu/arm,smmu.yaml        | 27 ++++++++++++++++++++++
> > > > > >     1 file changed, 27 insertions(+)