arm64: renesas: Add R-Car S4 Starter Kit support

Add support for the R-Car S4 Starter Kit with R8A779F4 SoC support.
This implementation natively uses OF_UPSTREAM to pull in most recent
DT. The defconfig is derived from S4 Spider, with reduced UART baud
rate to 921600 Bdps. The DT alias to rswitch is removed as the alias
should point to rswitch ports, not to rswitch itself, see [1].

[1] https://lore.kernel.org/linux-arm-kernel/20250118111344.361617-5-marek.vasut+renesas@mailbox.org/

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

arch/arm/dts/r8a779f4-s4sk-u-boot.dtsi

@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Device Tree Source extras for U-Boot for the S4SK board
+ *
+ * Copyright (C) 2024-2025 Renesas Electronics Corp.
+ */
+
+#include "r8a779f0-u-boot.dtsi"
+
+/ {
+	aliases {
+		spi0 = &rpc;
+		/delete-property/ ethernet0;
+	};
+};
+
+&pfc {
+	qspi0_pins: qspi0 {
+		groups = "qspi0_ctrl", "qspi0_data4";
+		function = "qspi0";
+	};
+};
+
+&rpc {
+	pinctrl-0 = <&qspi0_pins>;
+	pinctrl-names = "default";
+
+	#address-cells = <1>;
+	#size-cells = <0>;
+	spi-max-frequency = <40000000>;
+	status = "okay";
+
+	spi-flash@0 {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "s25fs512s", "jedec,spi-nor";
+		reg = <0>;
+		spi-tx-bus-width = <1>;
+		spi-rx-bus-width = <1>;
+		spi-max-frequency = <40000000>;
+	};
+};

arch/arm/mach-renesas/Kconfig.rcar4

@@ -54,6 +54,12 @@ config TARGET_SPIDER
 	help
 	  Support for Renesas R-Car Gen4 Spider platform
 
+config TARGET_S4SK
+	bool "S4SK board"
+	imply R8A779F0
+	help
+	  Support for Renesas R-Car Gen4 S4SK platform
+
 config TARGET_WHITEHAWK
 	bool "White Hawk board"
 	imply R8A779G0
@@ -70,6 +76,7 @@ endchoice
 
 source "board/renesas/falcon/Kconfig"
 source "board/renesas/spider/Kconfig"
+source "board/renesas/s4sk/Kconfig"
 source "board/renesas/whitehawk/Kconfig"
 source "board/renesas/grayhawk/Kconfig"
 

board/renesas/s4sk/Kconfig

@@ -0,0 +1,15 @@
+if TARGET_S4SK
+
+config SYS_SOC
+	default "renesas"
+
+config SYS_BOARD
+	default "s4sk"
+
+config SYS_VENDOR
+	default "renesas"
+
+config SYS_CONFIG_NAME
+	default "s4sk"
+
+endif

board/renesas/s4sk/MAINTAINERS

@@ -0,0 +1,7 @@
+S4SK BOARD
+M:	Marek Vasut <marek.vasut+renesas@mailbox.org>
+S:	Maintained
+F:	arch/arm/dts/r8a779f4*
+F:	board/renesas/s4sk/
+F:	configs/r8a779f4_s4sk_defconfig
+F:	include/configs/s4sk.h

board/renesas/s4sk/Makefile

@@ -0,0 +1,7 @@
+#
+# Copyright (C) 2025 Renesas Electronics Corp.
+#
+# SPDX-License-Identifier: GPL-2.0+
+#
+
+obj-y	:= s4sk.o

board/renesas/s4sk/s4sk.c

@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2025 Marek Vasut <marek.vasut+renesas@mailbox.org>
+ */
+
+#include <dm.h>
+#include <i2c.h>
+#include <malloc.h>
+#include <net-common.h>
+
+#define S4SK_FPGA_I2C_BUS			"i2c5"
+#define S4SK_FPGA_I2C_DEV_ADDR			0x70
+#define S4SK_FPGA_I2C_DEV_WIDTH			2
+#define S4SK_FPGA_I2C_MAC_COUNT			4
+#define S4SK_FPGA_I2C_MAC_OFFSET		0x58
+#define S4SK_FPGA_I2C_MAC_WIDTH			8
+
+int board_late_init(void)
+{
+	/*
+	 * Extract AVB and TSN0,1,2 MAC addresses from FPGA via I2C.
+	 *
+	 * In case a matching ethaddr/ethNaddr environment variable
+	 * is not set, set it, otherwise do not override it. This
+	 * allows users to set their own MAC addresses via ethaddr
+	 * and ethNaddr environment variables.
+	 *
+	 * The ethaddr/ethNaddr mapping follows Linux kernel DT aliases
+	 * ethernetN property assignment:
+	 * - ethaddr ..... TSN0 (IC104 connector)
+	 * - eth1addr .... TSN1 (IC101 connector)
+	 * - eth2addr .... TSN2 (Expansion connector)
+	 * - eth3addr .... AVB (CN1 connector)
+	 */
+	ofnode i2c_node = ofnode_path(S4SK_FPGA_I2C_BUS);
+	struct udevice *bus, *dev;
+	unsigned char enetaddr[6];
+	unsigned char macs[32];	/* Four MAC addresses in FPGA in total. */
+	int i, idx, j, ret;
+
+	ret = uclass_get_device_by_ofnode(UCLASS_I2C, i2c_node, &bus);
+	if (ret < 0) {
+		printf("s4sk: cannot find i2c bus (%d)\n", ret);
+		return 0;
+	}
+
+	ret = i2c_get_chip(bus, S4SK_FPGA_I2C_DEV_ADDR,
+			   S4SK_FPGA_I2C_DEV_WIDTH, &dev);
+	if (ret < 0) {
+		printf("s4sk: cannot find i2c chip (%d)\n", ret);
+		return 0;
+	}
+
+	ret = dm_i2c_read(dev, S4SK_FPGA_I2C_MAC_OFFSET, macs, sizeof(macs));
+	if (ret < 0) {
+		printf("s4sk: failed to read MAC addresses via i2c (%d)\n", ret);
+		return 0;
+	}
+
+	for (i = 0; i < S4SK_FPGA_I2C_MAC_COUNT; i++) {
+		/*
+		 * Remap TSN0,1,2 to ethaddr,eth1addr,eth2addr and
+		 * AVB to eth3addr to match Linux /aliases ethernetN
+		 * assignment, which starts with ethernet0 for TSN.
+		 */
+		idx = (i + 3) % 4;
+		ret = eth_env_get_enetaddr_by_index("eth", idx, enetaddr);
+		if (ret)	/* ethaddr is already set */
+			continue;
+
+		/* Byte-wise reverse the MAC address */
+		for (j = 0; j < sizeof(enetaddr); j++)
+			enetaddr[j] = macs[i * S4SK_FPGA_I2C_MAC_WIDTH + (5 - j)];
+
+		if (!is_valid_ethaddr(enetaddr)) {
+			printf("s4sk: MAC address %d in FPGA not valid (%pM)\n",
+			       i, enetaddr);
+			continue;
+		}
+
+		eth_env_set_enetaddr_by_index("eth", idx, enetaddr);
+	}
+
+	return 0;
+}

configs/r8a779f0_spider_defconfig

@@ -1,32 +1,11 @@
-#include <configs/renesas_rcar4.config>
+#include <configs/renesas_rcar4_s4.config>
 
 CONFIG_ARM=y
 CONFIG_ARCH_RENESAS=y
 CONFIG_RCAR_GEN4=y
-CONFIG_ENV_SIZE=0x40000
-CONFIG_ENV_OFFSET=0xD00000
-CONFIG_ENV_SECT_SIZE=0x40000
-CONFIG_DEFAULT_DEVICE_TREE="renesas/r8a779f0-spider"
 CONFIG_TARGET_SPIDER=y
-CONFIG_SYS_CLK_FREQ=20000000
-CONFIG_SYS_BOOT_GET_CMDLINE=y
-CONFIG_SYS_BARGSIZE=2048
+CONFIG_DEFAULT_DEVICE_TREE="renesas/r8a779f0-spider"
 CONFIG_BOOTCOMMAND="tftp 0x48080000 Image && tftp 0x48000000 Image-r8a779f0-spider.dtb && booti 0x48080000 - 0x48000000"
 CONFIG_DEFAULT_FDT_FILE="r8a779f0-spider.dtb"
-CONFIG_SYS_CBSIZE=2048
-CONFIG_CMD_PART=y
-CONFIG_CMD_UFS=y
-CONFIG_ENV_IS_IN_SPI_FLASH=y
-CONFIG_LBA48=y
-CONFIG_SYS_64BIT_LBA=y
-CONFIG_CLK_GPIO=y
-CONFIG_DM_PCA953X=y
-CONFIG_PHYLIB_10G=y
-CONFIG_PHY_MARVELL_10G=y
-CONFIG_RENESAS_ETHER_SWITCH=y
-CONFIG_PHY_R8A779F0_ETHERNET_SERDES=y
-CONFIG_SCSI=y
 CONFIG_BAUDRATE=1843200
-CONFIG_UFS=y
-CONFIG_UFS_RENESAS=y
-CONFIG_FS_FAT_MAX_CLUSTSIZE=131072
+CONFIG_DM_PCA953X=y

configs/r8a779f4_s4sk_defconfig

@@ -0,0 +1,11 @@
+#include <configs/renesas_rcar4_s4.config>
+
+CONFIG_ARM=y
+CONFIG_ARCH_RENESAS=y
+CONFIG_RCAR_GEN4=y
+CONFIG_TARGET_S4SK=y
+CONFIG_DEFAULT_DEVICE_TREE="renesas/r8a779f4-s4sk"
+CONFIG_BOOTCOMMAND="tftp 0x48080000 Image && tftp 0x48000000 Image-r8a779f4-s4sk.dtb && booti 0x48080000 - 0x48000000"
+CONFIG_DEFAULT_FDT_FILE="r8a779f4-s4sk.dtb"
+CONFIG_BAUDRATE=921600
+CONFIG_BOARD_LATE_INIT=y

configs/renesas_rcar4_s4.config

@@ -0,0 +1,23 @@
+#include <configs/renesas_rcar4.config>
+
+CONFIG_CLK_GPIO=y
+CONFIG_CMD_PART=y
+CONFIG_CMD_UFS=y
+CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_ENV_OFFSET=0xD00000
+CONFIG_ENV_SECT_SIZE=0x40000
+CONFIG_ENV_SIZE=0x40000
+CONFIG_FS_FAT_MAX_CLUSTSIZE=131072
+CONFIG_LBA48=y
+CONFIG_PHYLIB_10G=y
+CONFIG_PHY_MARVELL_10G=y
+CONFIG_PHY_R8A779F0_ETHERNET_SERDES=y
+CONFIG_RENESAS_ETHER_SWITCH=y
+CONFIG_SCSI=y
+CONFIG_SYS_64BIT_LBA=y
+CONFIG_SYS_BARGSIZE=2048
+CONFIG_SYS_BOOT_GET_CMDLINE=y
+CONFIG_SYS_CBSIZE=2048
+CONFIG_SYS_CLK_FREQ=20000000
+CONFIG_UFS=y
+CONFIG_UFS_RENESAS=y

doc/board/renesas/renesas.rst

@@ -168,6 +168,12 @@ Renesas is a SoC solutions provider for automotive and industrial applications.
      - arm64
      - r8a779f0_spider_defconfig
 
+   * -
+     - S4SK
+     - R8A779F4 (S4)
+     - arm64
+     - r8a779f4_s4sk_defconfig
+
    * -
      - White Hawk
      - R8A779G0 (V4H)

include/configs/s4sk.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * This file is S4SK board configuration.
+ *
+ * Copyright (C) 2024-2025 Renesas Electronics Corp.
+ */
+
+#ifndef __S4SK_H
+#define __S4SK_H
+
+#include "rcar-gen4-common.h"
+
+#endif /* __S4SK_H */