Re: [PATCH net-next v2 1/2] dt-bindings: net: qcom,bam-dmux: Add memory-region and qcom,vmid properties

[Vishnu Santhosh]

On 20-09-2026 04:06 pm, Krzysztof Kozlowski wrote:
> On Sun, Sep 20, 2026 at 08:32:29AM +0530, Vishnu Santhosh wrote:
> > Some Qualcomm SoCs, such as Shikra, run the modem in a separate security
> > domain with restricted access to system memory. BAM-DMUX DMA mappings
> Then this is specific to Shikra and should come with its compatible plus
> constraints per variant.

In v1, qcom,shikra-bam-dmux was used to select a different RX-buffer
allocation strategy. You asked me to drop it because the generic
qcom,bam-dmux compatible should cover that use case.

I followed that feedback in v2 and used memory-region plus qcom,vmid to
describe the optional firmware/security configuration instead.

Could you please clarify whether you now want qcom,shikra-bam-dmux restored
specifically as a schema discriminator, so memory-region and qcom,vmid
can be constrained to and required for Shikra, while the driver
continues to match the generic qcom,bam-dmux fallback?

> > must therefore be constrained to a designated region that can be shared
> > with the modem.
> >
> > Add an optional memory-region property to reference a restricted DMA
> > pool used for BAM-DMUX mappings, and a qcom,vmid property to identify the
> > remote execution environment that is granted access to the pool through
> > SCM.
> >
> > Require memory-region whenever qcom,vmid is specified.
> >
> > 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>
> > ---
> >   .../devicetree/bindings/net/qcom,bam-dmux.yaml     | 38 ++++++++++++++++++++++
> >   1 file changed, 38 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > index 33746c238513d72366bc52359fb10f275475b331..5351269b0ab72ede808ae47b55d57580af209038 100644
> > --- a/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > +++ b/Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
> > @@ -72,6 +72,24 @@ properties:
> >         - const: tx
> >         - const: rx
> >   
> > +  memory-region:
> > +    maxItems: 1
> > +    description:
> > +      Phandle to a reserved-memory node compatible with restricted-dma-pool.
> > +      The BAM-DMUX device uses the pool for DMA mappings.
> > +
> > +  qcom,vmid:
> > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > +    minItems: 1
> Drop

Agreed, will drop minItems in next revision.

> > +    maxItems: 1
> > +    items:
> > +      minimum: 1
> > +      maximum: 63
> > +    description:
> > +      VMID of the remote execution environment that is granted access to the
> > +      restricted DMA pool through SCM. The local execution environment is
> > +      retained automatically and must not be specified.
> > +
> >   required:
> >     - compatible
> >     - interrupts
> > @@ -81,12 +99,29 @@ required:
> >     - dmas
> >     - dma-names
> >   
> > +dependencies:
> > +  qcom,vmid: [ memory-region ]
> > +
> >   additionalProperties: false
> >   
> >   examples:
> >     - |
> > +    #include <dt-bindings/firmware/qcom,scm.h>
> >       #include <dt-bindings/interrupt-controller/irq.h>
> >   
> > +    reserved-memory {
> > +        #address-cells = <1>;
> > +        #size-cells = <1>;
> > +        ranges;
> > +
> > +        bam_dmux_pool: restricted-dma-pool {
> > +            compatible = "restricted-dma-pool";
> > +            size = <0x40000>;
> > +            alignment = <0x40000>;
> > +            alloc-ranges = <0x80000000 0x80000000>;
> > +        };
> > +    };
> This wasn't here before. Drop.
>
> Best regards,
> Krzysztof

Agreed, will drop changes to example in next revision.


Thanks,
Vishnu