Re: [RFC PATCH V1 1/6] dt-bindings: mt8183: Add binding for DIP shared memory

Rob Herring
2019-04-30T01:15:06Z

On Wed, Apr 17, 2019 at 06:45:06PM +0800, Frederic Chen wrote:
> This patch adds the binding for describing the shared memory
> used to exchange configuration and tuning data between the
> co-processor and Digital Image Processing (DIP) unit of the
> camera ISP system on Mediatek SoCs.
>
> Signed-off-by: Frederic Chen <frederic.chen@mediatek.com>
> ---
> .../mediatek,reserve-memory-dip_smem.txt | 45 +++++++++++++++++++
> 1 file changed, 45 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt b/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
> new file mode 100644
> index 000000000000..64c001b476b9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/reserved-memory/mediatek,reserve-memory-dip_smem.txt
> @@ -0,0 +1,45 @@
> +Mediatek DIP Shared Memory binding
> +
> +This binding describes the shared memory, which serves the purpose of
> +describing the shared memory region used to exchange data between Digital
> +Image Processing (DIP) and co-processor in Mediatek SoCs.
> +
> +The co-processor doesn't have the iommu so we need to use the physical
> +address to access the shared buffer in the firmware.
> +
> +The Digital Image Processing (DIP) can access memory through mt8183 IOMMU so
> +it can use dma address to access the memory region.
> +(See iommu/mediatek,iommu.txt for the detailed description of Mediatek IOMMU)
> +
> +
> +Required properties:
> +
> +- compatible: must be "mediatek,reserve-memory-dip_smem"

Don't use '_'.

> +
> +- reg: required for static allocation (see reserved-memory.txt for
> + the detailed usage)
> +
> +- alloc-range: required for dynamic allocation. The range must
> + between 0x00000400 and 0x100000000 due to the co-processer's
> + addressing limitation

Generally, you should pick either static or dynamic allocation for a
given binding. Static if there's some address restriction or sharing,
dynamic if not.

Sounds like static in this case.

> +
> +- size: required for dynamic allocation. The unit is bytes.
> + If you want to enable the full feature of Digital Processing Unit,
> + you need 20 MB at least.
> +
> +
> +Example:
> +
> +The following example shows the DIP shared memory setup for MT8183.
> +
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + ranges;
> + reserve-memory-dip_smem {
> + compatible = "mediatek,reserve-memory-dip_smem";
> + size = <0 0x1400000>;
> + alignment = <0 0x1000>;
> + alloc-ranges = <0 0x40000000 0 0x50000000>;
> + };
> + };
> --
> 2.18.0
>