ARM: dts: meson8b: fix the Ethernet data line signals in eth_rgmii_pins

[ Upstream commit 29f0023d ]

According to the Odroid-C1+ schematics the Ethernet TXD1 signal is
routed to GPIOH_5 and the TXD0 signal is routed to GPIOH_6.
The public S805 datasheet shows that TXD0 can be routed to DIF_2_P and
TXD1 can be routed to DIF_2_N instead.

The pin groups eth_txd0_0 (GPIOH_6) and eth_txd0_1 (DIF_2_P) are both
configured as Ethernet TXD0 and TXD1 data lines in meson8b.dtsi. At the
same time eth_txd1_0 (GPIOH_5) and eth_txd1_1 (DIF_2_N) are configured
as TXD0 and TXD1 data lines as well.
This results in a bad Ethernet receive performance. Presumably this is
due to the eth_txd0 and eth_txd1 signal being routed to the wrong pins.
As a result of that data can only be transmitted on eth_txd2 and
eth_txd3. However, I have no scope to fully confirm this assumption.

The vendor u-boot sources for Odroid-C1 use the following Ethernet
pinmux configuration:
  SET_CBUS_REG_MASK(PERIPHS_PIN_MUX_6, 0x3f4f);
  SET_CBUS_REG_MASK(PERIPHS_PIN_MUX_7, 0xf00000);
This translates to the following pin groups in the mainline kernel:
- register 6 bit  0: eth_rxd1 (DIF_0_P)
- register 6 bit  1: eth_rxd0 (DIF_0_N)
- register 6 bit  2: eth_rx_dv (DIF_1_P)
- register 6 bit  3: eth_rx_clk (DIF_1_N)
- register 6 bit  6: eth_tx_en (DIF_3_P)
- register 6 bit  8: eth_ref_clk (DIF_3_N)
- register 6 bit  9: eth_mdc (DIF_4_P)
- register 6 bit 10: eth_mdio_en (DIF_4_N)
- register 6 bit 11: eth_tx_clk (GPIOH_9)
- register 6 bit 12: eth_txd2 (GPIOH_8)
- register 6 bit 13: eth_txd3 (GPIOH_7)
- register 7 bit 20: eth_txd0_0 (GPIOH_6)
- register 7 bit 21: eth_txd1_0 (GPIOH_5)
- register 7 bit 22: eth_rxd3 (DIF_2_P)
- register 7 bit 23: eth_rxd2 (DIF_2_N)

Drop the eth_txd0_1 and eth_txd1_1 groups from eth_rgmii_pins to fix the
Ethernet transmit performance on Odroid-C1. Also add the eth_rxd2 and
eth_rxd3 groups so we don't rely on the bootloader to set them up.

iperf3 statistics before this change:
- transmitting from Odroid-C1: 741 Mbits/sec (0 retries)
- receiving on Odroid-C1: 199 Mbits/sec (1713 retries)

iperf3 statistics after this change:
- transmitting from Odroid-C1: 667 Mbits/sec (0 retries)
- receiving on Odroid-C1: 750 Mbits/sec (0 retries)

Fixes: b9644654 ("ARM: dts: meson8b: extend ethernet controller description")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Emiliano Ingrassia <ingrassia@epigenesys.com>
Cc: Linus Lüssing <linus.luessing@c0d3.blue>
Tested-by: Emiliano Ingrassia <ingrassia@epigenesys.com>
Reviewed-by: Emiliano Ingrassia <ingrassia@epigenesys.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/arm/boot/dts/meson8b.dtsi

@@ -207,9 +207,7 @@ mux {
 				groups = "eth_tx_clk",
 					 "eth_tx_en",
 					 "eth_txd1_0",
-					 "eth_txd1_1",
 					 "eth_txd0_0",
-					 "eth_txd0_1",
 					 "eth_rx_clk",
 					 "eth_rx_dv",
 					 "eth_rxd1",
@@ -218,7 +216,9 @@ mux {
 					 "eth_mdc",
 					 "eth_ref_clk",
 					 "eth_txd2",
-					 "eth_txd3";
+					 "eth_txd3",
+					 "eth_rxd3",
+					 "eth_rxd2";
 				function = "ethernet";
 			};
 		};