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

[Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>]

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@oss.qualcomm.com>
>> Signed-off-by: Deepak Kumar Singh <deepak.singh@oss.qualcomm.com>
>> Signed-off-by: Vishnu Santhosh <vishnu.santhosh@oss.qualcomm.com>
>> ---
>>   .../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