linux-kernel - [PATCH v1 5/8] riscv: dts: starfive: Add pool for coherent DMA memory on JH7100 boards

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Date:   Mon, 27 Nov 2023 00:27:43 +0100
From:   Emil Renner Berthing <emil.renner.berthing@...onical.com>
To:     linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Conor Dooley <conor@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
Subject: [PATCH v1 5/8] riscv: dts: starfive: Add pool for coherent DMA memory on JH7100 boards

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.

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@...onical.com>
---
 .../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..3af88e6970a3 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@...00000 {
+			reg = <0x0 0xfa000000 0x0 0x1000000>;
+			no-map;
+		};
+
+		linux,dma@...a000000 {
+			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 {
-- 
2.40.1