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

From: Rob Herring <[email-masked]>
Date: Mon, 29 Apr 2019 20:15:06 -0500

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 <[email-masked]>
> ---
>  .../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
> 

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