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

Hi Krzysztof,

On Sun, Sep 20, 2026 at 12:36 PM Krzysztof Kozlowski [off-list ref] 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.

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:

I can see several existing drivers, along with a few ongoing series,
using this same property. Instead of redefining it in every binding,
should we consider defining the prop/type once in a common soc/qcom
schema and reusing it across bindings?

quoted

+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    minItems: 1

Drop

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