Re: [PATCH v4 03/19] dt-bindings: display: mediatek: add EXDMA yaml for MT8196

["CK Hu (胡俊光)" <ck.hu@mediatek.com>]

Hi, Rob and Krzysztof:

On Thu, 2025-08-28 at 16:06 +0800, Paul Chen wrote:
> From: Paul-pl Chen <paul-pl.chen@mediatek.com>
> 
> Add mediatek,exdma.yaml to support EXDMA for MT8196.
> The MediaTek display overlap extended DMA engine, namely
> OVL_EXDMA or EXDMA, primarily functions as a DMA engine
> for reading data from DRAM with various DRAM footprints
> and data formats.
> 
> Signed-off-by: Paul-pl Chen <paul-pl.chen@mediatek.com>
> ---
>  .../bindings/dma/mediatek,exdma.yaml          | 68 +++++++++++++++++++
>  1 file changed, 68 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/dma/mediatek,exdma.yaml
> 
> diff --git a/Documentation/devicetree/bindings/dma/mediatek,exdma.yaml b/Documentation/devicetree/bindings/dma/mediatek,exdma.yaml
> new file mode 100644
> index 000000000000..eabf0cfc839e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/mediatek,exdma.yaml
> @@ -0,0 +1,68 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: https://urldefense.com/v3/__http://devicetree.org/schemas/dma/mediatek,exdma.yaml*__;Iw!!CTRNKA9wMg0ARbw!mjQH2qNKhXsl47d3xz2_Qmo7Wadq5-kD0GJaAVjh7XY8W3NgI_dDpBNinME7NVW1PKdO9IEUsObOTugjypqo5j8$ 
> +$schema: https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!mjQH2qNKhXsl47d3xz2_Qmo7Wadq5-kD0GJaAVjh7XY8W3NgI_dDpBNinME7NVW1PKdO9IEUsObOTugj3hMMPhU$ 
> +
> +title: MediaTek display overlap extended DMA engine
> +
> +maintainers:
> +  - Chun-Kuang Hu <chunkuang.hu@kernel.org>
> +  - Philipp Zabel <p.zabel@pengutronix.de>
> +
> +description:
> +  The MediaTek display overlap extended DMA engine, namely OVL_EXDMA or EXDMA,
> +  primarily functions as a DMA engine for reading data from DRAM with various
> +  DRAM footprints and data formats. For input sources in certain color formats
> +  and color domains, OVL_EXDMA also includes a color transfer function
> +  to process pixels into a consistent color domain.
> +
> +properties:
> +  compatible:
> +    const: mediatek,mt8196-exdma
> +
> +  reg:
> +    maxItems: 1
> +
> +  clocks:
> +    maxItems: 1
> +
> +  power-domains:
> +    maxItems: 1
> +
> +  mediatek,larb:
> +    $ref: /schemas/types.yaml#/definitions/phandle
> +    description: |
> +      A phandle to the local arbiters node in the current SoCs.
> +      Refer to bindings/memory-controllers/mediatek,smi-larb.yaml.

In MT8196, the data path that EXDMA access DRAM data is shown below.

EXDMA (dma device) <-> LARB <-> SMMU (mmu device) <-> DRAM

In MT8195, the data path that OVL access DRAM data is shown below.

OVL (dma device) <-> LARB <-> IOMMU_VPP (mmu device) <-> DRAM

These two are similar, and LARB works like a bus.

In MT8195 device tree [1] (upstream), OVL has an iommus property pointing to IOMMU_VPP,

and IOMMU_VPP has a larbs property pointing to LARB

                iommu_vpp: iommu@14018000 {

                         compatible = "mediatek,mt8195-iommu-vpp";

                         reg = <0 0x14018000 0 0x1000>;

                         mediatek,larbs = <&larb1 &larb3 &larb4 &larb6 &larb8

                                            &larb12 &larb14 &larb16 &larb18

                                            &larb20 &larb22 &larb23 &larb26

                                            &larb27>;

                         interrupts = <GIC_SPI 594 IRQ_TYPE_LEVEL_HIGH 0>;

                         clocks = <&vppsys0 CLK_VPP0_SMI_IOMMU>;

                         clock-names = "bclk";

                         #iommu-cells = <1>;

                         power-domains = <&spm MT8195_POWER_DOMAIN_VPPSYS0>;

                };

                display@14009000 {

                         compatible = "mediatek,mt8195-mdp3-ovl";

                         reg = <0 0x14009000 0 0x1000>;

                         interrupts = <GIC_SPI 586 IRQ_TYPE_LEVEL_HIGH 0>;

                         mediatek,gce-client-reg = <&gce1 SUBSYS_1400XXXX 0x9000 0x1000>;

                         clocks = <&vppsys0 CLK_VPP0_MDP_OVL>;

                         power-domains = <&spm MT8195_POWER_DOMAIN_VPPSYS0>;

                         iommus = <&iommu_vpp M4U_PORT_L4_MDP_OVL>;

                };

In MT8196 [2] (this patch), EXDMA has an iommus property pointing to SMMU and a larbs property pointing to LARB.

                 mm_smmu: iommu@30800000 {

                         compatible = "mediatek,mt8196-mm-smmu", "arm,smmu-v3";

                         reg = <0 0x30800000 0 0x1e0000>;

                         interrupts = <GIC_SPI 477 IRQ_TYPE_EDGE_RISING 0>;

                         interrupt-names = "combined";

                         #iommu-cells = <1>;

                 };

                 disp_ovl0_exdma2: dma-controller@32850000 {

                         compatible = "mediatek,mt8196-exdma";

                         reg = <0 0x32850000 0 0x1000>;

                         clocks = <&ovlsys_config_clk CLK_OVL_EXDMA2_DISP>;

                         power-domains = <&hfrpsys MT8196_POWER_DOMAIN_OVL0_DORMANT>;

                         mediatek,larb = <&smi_larb0>;

                         iommus = <&mm_smmu 144>;

                         #dma-cells = <1>;

                 };

Both hardware data path is similar, but LARB is pointed by IOMMU device in MT8195 and LARB is pointed by DMA device in MT8196.

Should LARB be pointed by the same device (DMA device or IOMMU device)?

Or another way to describe these three device?

 

[1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/arch/arm64/boot/dts/mediatek/mt8195.dtsi?h=next-20250626

[2] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/6253459/2/arch/arm64/boot/dts/mediatek/mt8196.dtsi#3127

 

Regards,

CK

> +
> +  iommus:
> +    maxItems: 1
> +
> +  '#dma-cells':
> +    const: 1
> +
> +required:
> +  - compatible
> +  - reg
> +  - clocks
> +  - power-domains
> +  - mediatek,larb
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    soc {
> +        #address-cells = <2>;
> +        #size-cells = <2>;
> +
> +        exdma: dma-controller@32850000 {
> +            compatible = "mediatek,mt8196-exdma";
> +            reg = <0 0x32850000 0 0x1000>;
> +            clocks = <&ovlsys_config_clk 13>;
> +            power-domains = <&hfrpsys 12>;
> +            iommus = <&mm_smmu 144>;
> +            #dma-cells = <1>;
> +        };
> +    };