Add the binding for smi-sub-common. The SMI block diagram like this:

        IOMMU
         |  |
      smi-common
  ------------------
  |      ....      |
 larb0           larb7   <-max is 8

The smi-common connects with smi-larb and IOMMU. The maximum larbs number
that connects with a smi-common is 8. If the engines number is over 8,
sometimes we use a smi-sub-common which is nearly same with smi-common.
It supports up to 8 input and 1 output(smi-common has 2 output)

Something like:

        IOMMU
         |  |
      smi-common
  ---------------------
  |      |          ...
larb0  sub-common   ...   <-max is 8
      -----------
       |    |    ...   <-max is 8 too.
     larb2 larb5

We don't need extra SW setting for smi-sub-common, only the sub-common has
special clocks need to enable when the engines access dram.

If it is sub-common, it should have a "mediatek,smi" phandle to point to
its smi-common. meanwhile the sub-common only has one gals clock.

Additionally, add a new property "mediatek,smi_sub_common" for this
sub-common, this is needed in the IOMMU driver in which we create a device
link between smi-common and the IOMMU device. If we add the smi-sub-common
here, the IOMMU driver still need to find the smi-common device. thus,
add this bool property to indicate if it is sub-common.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
---
change note:
a. change mediatek, smi type from phandle-array to phandle from Rob.
b. Add a new bool property (mediatek,smi_sub_common) to indicate this is
   smi-sub-common. the reason is as above.
---
 .../mediatek,smi-common.yaml                  | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/devicetree/bindings/memory-controllers/mediatek,smi-common.yaml b/Documentation/devicetree/bindings/memory-controllers/mediatek,smi-common.yaml
index 602592b6c3f5..26bb9903864b 100644
--- a/Documentation/devicetree/bindings/memory-controllers/mediatek,smi-common.yaml
+++ b/Documentation/devicetree/bindings/memory-controllers/mediatek,smi-common.yaml

@@ -38,6 +38,7 @@ properties:
           - mediatek,mt8192-smi-common
           - mediatek,mt8195-smi-common-vdo
           - mediatek,mt8195-smi-common-vpp
+          - mediatek,mt8195-smi-sub-common
 
       - description: for mt7623
         items:

@@ -67,6 +68,14 @@ properties:
     minItems: 2
     maxItems: 4
 
+  mediatek,smi:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description: a phandle to the smi-common node above. Only for sub-common.
+
+  mediatek,smi_sub_common:

+    type: boolean
+    description: Indicate if this is smi-sub-common.
+
 required:
   - compatible
   - reg

@@ -93,6 +102,27 @@ allOf:
             - const: smi
             - const: async
 
+  - if:  # only for sub common
+      properties:
+        compatible:
+          contains:
+            enum:
+              - mediatek,mt8195-smi-sub-common
+    then:
+      required:
+        - mediatek,smi
+        - mediatek,smi_sub_common
+      properties:
+        clock:
+          items:
+            minItems: 3
+            maxItems: 3
+        clock-names:
+          items:
+            - const: apb
+            - const: smi
+            - const: gals0