[PATCH v3 13/13] arm64: dts: qcom: sm8750: Add Iris 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/

The video-codec node includes address-cells, size-cells and dma-ranges
to declare 1:1 mapping for DMA translation to 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>
---
 arch/arm64/boot/dts/qcom/sm8750.dtsi | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/boot/dts/qcom/sm8750.dtsi b/arch/arm64/boot/dts/qcom/sm8750.dtsi
index eb3a6990ec30ba3ca1c3fe468ffdb4e9df00174d..206ac22cab2c0dfabc1ca5f619f598e4823776de 100644
--- a/arch/arm64/boot/dts/qcom/sm8750.dtsi
+++ b/arch/arm64/boot/dts/qcom/sm8750.dtsi
@@ -3026,8 +3026,6 @@ iris: video-codec@aa00000 {
 				      "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>,
@@ -3060,6 +3058,10 @@ &config_noc SLAVE_VENUS_CFG QCOM_ICC_TAG_ACTIVE_ONLY>,
 				      "core",
 				      "vcodec0_core";
 
+			#address-cells = <1>;
+			#size-cells = <1>;
+			dma-ranges = <0x0 0x0 0x0 0xe0000000>;
+
 			/*
 			 * IRIS firmware is signed by vendors, only
 			 * enable in boards where the proper signed firmware
@@ -3067,6 +3069,15 @@ &config_noc SLAVE_VENUS_CFG QCOM_ICC_TAG_ACTIVE_ONLY>,
 			 */
 			status = "disabled";
 
+			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