[PATCH v4 03/13] dt-bindings: media: qcom,sm8750-iris: Add context bank subnodes

[Vikash Garodia]

The VPU issues DMA through several SMMU streams, and the hardware does
not give every stream the same addressable range. The non-pixel stream
cannot address the low 600MB of IOVA space, while the pixel stream can
address the full range:
    +-----------------------------------------------------------+
    | non-pixel stream addressable range (600 MB - 3.5 GB)      |
    | 0x25800000 - 0xe0000000                                   |
    +-----------------------------------------------------------+
    | pixel stream addressable range (0 - 3.5 GB)               |
    | 0x00000000 - 0xe0000000                                   |
    +-----------------------------------------------------------+
A single "iommus" property on the video-codec node puts every stream in
one IOMMU domain sharing one IOVA allocator, so nothing restricts a
non-pixel buffer to avoid 0 to 600MB. Once an allocation lands below
that boundary the hardware faults, which shows up as unhandled SMMU page
faults and spontaneous reboots:
https://gitlab.freedesktop.org/drm/msm/-/work_items/100

Given that the address range restriction is for specific VPU stream, it
should be ideally be moved to that stream. To achieve the same, a subset
of streams is now represented as subnodes, so that each can be
associated with its respective addressable range. The design was discussed
and agreed by mainatiners here
https://lore.kernel.org/all/c7b956a9-d3e8-4e18-b780-5d08f5cd2ca1@xxxxxxxxxx

In the past, this limitation was addressed with an iommu-map approach,
with the iris driver dynamically creating the devices. That approach
was later concluded to be a hack to avoid having subnodes, and was NAKed
by the iommu maintainers. It was discussed in detail here:
https://lore.kernel.org/all/c7b956a9-d3e8-4e18-b780-5d08f5cd2ca1@xxxxxxxxxx/

Update example to the subnode form. Doing so, it picks up the supporting
properties needed on the video-codec node, address-cells, size-cells and
dma-ranges to declare 1:1 DMA translation into the parent.

Co-developed-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
Signed-off-by: Vishnu Reddy <busanna.reddy@xxxxxxxxxxxxxxxx>
Signed-off-by: Vikash Garodia <vikash.garodia@xxxxxxxxxxxxxxxx>
---
 .../devicetree/bindings/media/qcom,sm8750-iris.yaml      | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/media/qcom,sm8750-iris.yaml b/Documentation/devicetree/bindings/media/qcom,sm8750-iris.yaml
index c42d3470bdac796cc878090e65becf6b62bd80ca..b6d5ded1aae6a1a6836c2c24b1dae548cdc6f9d2 100644
--- a/Documentation/devicetree/bindings/media/qcom,sm8750-iris.yaml
+++ b/Documentation/devicetree/bindings/media/qcom,sm8750-iris.yaml
@@ -72,7 +72,6 @@ required:
   - dma-coherent
   - interconnects
   - interconnect-names
-  - iommus
   - power-domain-names
   - resets
   - reset-names
@@ -110,8 +109,6 @@ examples:
                       "vcodec0_core_freerun";
 
         dma-coherent;
-        iommus = <&apps_smmu 0x1940 0>,
-                 <&apps_smmu 0x1947 0>;
 
         interconnects = <&gem_noc MASTER_APPSS_PROC QCOM_ICC_TAG_ACTIVE_ONLY
                          &config_noc SLAVE_VENUS_CFG QCOM_ICC_TAG_ACTIVE_ONLY>,
@@ -144,6 +141,19 @@ examples:
                       "core",
                       "vcodec0_core";
 
+        #address-cells = <1>;
+        #size-cells = <1>;
+        dma-ranges = <0x0 0x0 0xe0000000>;
+
+        non-pixel {
+            iommus = <&apps_smmu 0x1940 0x0>;
+            iommu-ranges = <0x25800000 0xba800000>;
+        };
+
+        pixel {
+            iommus = <&apps_smmu 0x1947 0x0>;
+        };
+
         iris_opp_table: opp-table {
             compatible = "operating-points-v2";
 

-- 
2.34.1