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

On 20-09-2026 04:06 pm, Krzysztof Kozlowski wrote:

On Sun, Sep 20, 2026 at 08:32:29AM +0530, Vishnu Santhosh wrote:

quoted

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?

quoted

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 <redacted>
Signed-off-by: Deepak Kumar Singh <redacted>
Signed-off-by: Vishnu Santhosh <redacted>
---
  .../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.

quoted

+    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