Re: [PATCH v2 08/12] riscv: dts: starfive: Add pool for coherent DMA memory on JH7100 boards

[Emil Renner Berthing]

Cristian Ciocaltea wrote:
> From: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
>
> The StarFive JH7100 SoC has non-coherent device DMAs, but most drivers
> expect to be able to allocate coherent memory for DMA descriptors and
> such. However on the JH7100 DDR memory appears twice in the physical
> memory map, once cached and once uncached:
>
>   0x00_8000_0000 - 0x08_7fff_ffff : Off chip DDR memory, cached
>   0x10_0000_0000 - 0x17_ffff_ffff : Off chip DDR memory, uncached
>
> To use this uncached region we create a global DMA memory pool there and
> reserve the corresponding area in the cached region.
>
> However the uncached region is fully above the 32bit address limit, so add
> a dma-ranges map so the DMA address used for peripherals is still in the
> regular cached region below the limit.

Adding these nodes to the device tree won't actually do anything without
enabling CONFIG_DMA_GLOBAL_POOL as is done here:

https://github.com/esmil/linux/commit/e14ad9ff67fd51dcc76415d4cc7f3a30ffcba379

>
> Link: https://github.com/starfive-tech/JH7100_Docs/blob/main/JH7100%20Data%20Sheet%20V01.01.04-EN%20(4-21-2021).pdf
> Signed-off-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> ---
>  .../boot/dts/starfive/jh7100-common.dtsi      | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/arch/riscv/boot/dts/starfive/jh7100-common.dtsi b/arch/riscv/boot/dts/starfive/jh7100-common.dtsi
> index b93ce351a90f..504c73f01f14 100644
> --- a/arch/riscv/boot/dts/starfive/jh7100-common.dtsi
> +++ b/arch/riscv/boot/dts/starfive/jh7100-common.dtsi
> @@ -39,6 +39,30 @@ led-ack {
>  			label = "ack";
>  		};
>  	};
> +
> +	reserved-memory {
> +		#address-cells = <2>;
> +		#size-cells = <2>;
> +		ranges;
> +
> +		dma-reserved {
> +			reg = <0x0 0xfa000000 0x0 0x1000000>;
> +			no-map;
> +		};
> +
> +		linux,dma {
> +			compatible = "shared-dma-pool";
> +			reg = <0x10 0x7a000000 0x0 0x1000000>;
> +			no-map;
> +			linux,dma-default;
> +		};
> +	};
> +
> +	soc {
> +		dma-ranges = <0x00 0x80000000 0x00 0x80000000 0x00 0x7a000000>,
> +			     <0x00 0xfa000000 0x10 0x7a000000 0x00 0x01000000>,
> +			     <0x00 0xfb000000 0x00 0xfb000000 0x07 0x85000000>;
> +	};
>  };
>
>  &gpio {
> --
> 2.42.0
>