[PATCH v1] riscv: dts: thead: Fix TH1520 emmc and shdci clock rate

[bigunclemax at gmail.com]

From: Maksim Kiselev <bigunclemax at gmail.com>

In accordance with LicheePi 4A BSP the clock that comes to emmc/sdhci
is 198Mhz.

But changing from fixed-clock to CLK_EMMC_SDIO leads to increasing input
clock from 198Mhz to 792Mhz. Because the CLK_EMMC_SDIO is actually 792Mhz.

Therefore calculation of output SDCLK is incorrect now.
The mmc driver sets the divisor to 4 times larger than it should be
and emmc/sd works 4 times slower.

This can be confirmed with fio test:
Sequential read of emmc with fixed 198Mz clock:
READ: bw=289MiB/s (303MB/s)

Sequential read with CLK_EMMC_SDIO clock:
READ: bw=82.6MiB/s (86.6MB/s)

Let's fix this issue by providing fixed-factor-clock that divides
CLK_EMMC_SDIO by 4 for emmc/sd nodes.

Fixes: 03a20182e1e0 ("riscv: dts: thead: change TH1520 mmc nodes to use clock controller")
Signed-off-by: Maksim Kiselev <bigunclemax at gmail.com>
---
 arch/riscv/boot/dts/thead/th1520.dtsi | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
index acfe030e803a..6c20965cd10c 100644
--- a/arch/riscv/boot/dts/thead/th1520.dtsi
+++ b/arch/riscv/boot/dts/thead/th1520.dtsi
@@ -229,6 +229,14 @@ stmmac_axi_config: stmmac-axi-config {
 		snps,blen = <0 0 64 32 0 0 0>;
 	};
 
+	sdhci_clk: sdhci-clock {
+		compatible = "fixed-factor-clock";
+		clocks = <&clk CLK_EMMC_SDIO>;
+		#clock-cells = <0>;
+		clock-div = <4>;
+		clock-mult = <1>;
+	};
+
 	soc {
 		compatible = "simple-bus";
 		interrupt-parent = <&plic>;
@@ -328,7 +336,7 @@ emmc: mmc at ffe7080000 {
 			compatible = "thead,th1520-dwcmshc";
 			reg = <0xff 0xe7080000 0x0 0x10000>;
 			interrupts = <62 IRQ_TYPE_LEVEL_HIGH>;
-			clocks = <&clk CLK_EMMC_SDIO>;
+			clocks = <&sdhci_clk>;
 			clock-names = "core";
 			status = "disabled";
 		};
@@ -337,7 +345,7 @@ sdio0: mmc at ffe7090000 {
 			compatible = "thead,th1520-dwcmshc";
 			reg = <0xff 0xe7090000 0x0 0x10000>;
 			interrupts = <64 IRQ_TYPE_LEVEL_HIGH>;
-			clocks = <&clk CLK_EMMC_SDIO>;
+			clocks = <&sdhci_clk>;
 			clock-names = "core";
 			status = "disabled";
 		};
@@ -346,7 +354,7 @@ sdio1: mmc at ffe70a0000 {
 			compatible = "thead,th1520-dwcmshc";
 			reg = <0xff 0xe70a0000 0x0 0x10000>;
 			interrupts = <71 IRQ_TYPE_LEVEL_HIGH>;
-			clocks = <&clk CLK_EMMC_SDIO>;
+			clocks = <&sdhci_clk>;
 			clock-names = "core";
 			status = "disabled";
 		};
-- 
2.45.2