Re: [PATCH v2] dt-bindings: dma: qcom,bam-dma: Allow memory-region property

[Vishnu Santhosh]

On 20-09-2026 04:02 pm, Krzysztof Kozlowski wrote:
> On Sun, Sep 20, 2026 at 08:03:05AM +0530, Vishnu Santhosh wrote:
> > Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
> > domain, preventing it from accessing BAM descriptor FIFOs allocated from
> > arbitrary host memory.
> >
> > Add an optional memory-region property to constrain DMA allocations made
> > by the BAM DMA controller to a restricted DMA pool. Access permissions
> > for the remote execution environment are managed separately.
> >
> > Co-developed-by: Deepak Kumar Singh <deepak.singh@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Deepak Kumar Singh <deepak.singh@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Vishnu Santhosh <vishnu.santhosh@xxxxxxxxxxxxxxxx>
> > ---
> > Changes in v2:
> > - Replace the qcom,vmid property and BAM DMA driver SCM assignment with
> >    the standard memory-region restricted DMA pool mechanism.
> > - Rely on generic DMA handling to constrain descriptor FIFO allocations
> >    to the restricted pool.
> > - Drop the Shikra-specific BAM compatible and all BAM DMA driver changes.
> > - Link to v1: https://lore.kernel.org/r/20260714-qcom-bam-dma-vmid-ext-v1-0-cef87c57b7dc@xxxxxxxxxxxxxxxx
> And a reason to drop review?

The binding was substantially redesigned in v2, so I did not carry Rob's Reviewed-by.
I will explicitly mention that in the v2 changelog in next revision.

> > ---
> >   .../devicetree/bindings/dma/qcom,bam-dma.yaml       | 21 +++++++++++++++++++++
> >   1 file changed, 21 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml b/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml
> > index e72adc172af102d8f400044ea0dc32db6b2365be..1e4324799f2b3b8a9ebf9f084e457e66aad20d28 100644
> > --- a/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml
> > +++ b/Documentation/devicetree/bindings/dma/qcom,bam-dma.yaml
> > @@ -50,6 +50,13 @@ properties:
> >       minItems: 1
> >       maxItems: 7
> >   
> > +  memory-region:
> > +    maxItems: 1
> > +    description:
> > +      Phandle to a reserved-memory node compatible with restricted-dma-pool.
> > +      The BAM DMA controller uses the pool for DMA allocations, including
> > +      channel descriptor FIFOs.
> > +
> >     num-channels:
> >       $ref: /schemas/types.yaml#/definitions/uint32
> >       description:
> > @@ -137,6 +144,20 @@ examples:
> >               qcom,num-ees = <4>;
> >               num-channels = <20>;
> >               qcom,controlled-remotely;
> > +            memory-region = <&bam_dmux_pool>;
> > +        };
> > +    };
> > +
> > +    reserved-memory {
> No need for this.
>
> Best regards,
> Krzysztof

Agreed. I will drop the changes to the example in v3.

Thanks,
Vishnu