--- zzzz-none-000/linux-3.10.107/arch/mips/ralink/early_printk.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/mips/ralink/early_printk.c	2021-02-04 17:41:59.000000000 +0000
@@ -12,21 +12,26 @@
 #include <asm/addrspace.h>
 
 #ifdef CONFIG_SOC_RT288X
-#define EARLY_UART_BASE         0x300c00
+#define EARLY_UART_BASE		0x300c00
+#define CHIPID_BASE		0x300004
+#elif defined(CONFIG_SOC_MT7621)
+#define EARLY_UART_BASE		0x1E000c00
+#define CHIPID_BASE		0x1E000004
 #else
-#define EARLY_UART_BASE         0x10000c00
+#define EARLY_UART_BASE		0x10000c00
+#define CHIPID_BASE		0x10000004
 #endif
 
-#define UART_REG_RX             0x00
-#define UART_REG_TX             0x04
-#define UART_REG_IER            0x08
-#define UART_REG_IIR            0x0c
-#define UART_REG_FCR            0x10
-#define UART_REG_LCR            0x14
-#define UART_REG_MCR            0x18
-#define UART_REG_LSR            0x1c
+#define MT7628_CHIP_NAME1	0x20203832
+
+#define UART_REG_TX		0x04
+#define UART_REG_LCR		0x0c
+#define UART_REG_LSR		0x14
+#define UART_REG_LSR_RT2880	0x1c
 
 static __iomem void *uart_membase = (__iomem void *) KSEG1ADDR(EARLY_UART_BASE);
+static __iomem void *chipid_membase = (__iomem void *) KSEG1ADDR(CHIPID_BASE);
+static int init_complete;
 
 static inline void uart_w32(u32 val, unsigned reg)
 {
@@ -38,11 +43,47 @@
 	return __raw_readl(uart_membase + reg);
 }
 
+static inline int soc_is_mt7628(void)
+{
+	return IS_ENABLED(CONFIG_SOC_MT7620) &&
+		(__raw_readl(chipid_membase) == MT7628_CHIP_NAME1);
+}
+
+static void find_uart_base(void)
+{
+	int i;
+
+	if (!soc_is_mt7628())
+		return;
+
+	for (i = 0; i < 3; i++) {
+		u32 reg = uart_r32(UART_REG_LCR + (0x100 * i));
+
+		if (!reg)
+			continue;
+
+		uart_membase = (__iomem void *) KSEG1ADDR(EARLY_UART_BASE +
+							  (0x100 * i));
+		break;
+	}
+}
+
 void prom_putchar(unsigned char ch)
 {
-	while ((uart_r32(UART_REG_LSR) & UART_LSR_THRE) == 0)
-		;
-	uart_w32(ch, UART_REG_TX);
-	while ((uart_r32(UART_REG_LSR) & UART_LSR_THRE) == 0)
-		;
+	if (!init_complete) {
+		find_uart_base();
+		init_complete = 1;
+	}
+
+	if (IS_ENABLED(CONFIG_SOC_MT7621) || soc_is_mt7628()) {
+		uart_w32(ch, UART_TX);
+		while ((uart_r32(UART_REG_LSR) & UART_LSR_THRE) == 0)
+			;
+	} else {
+		while ((uart_r32(UART_REG_LSR_RT2880) & UART_LSR_THRE) == 0)
+			;
+		uart_w32(ch, UART_REG_TX);
+		while ((uart_r32(UART_REG_LSR_RT2880) & UART_LSR_THRE) == 0)
+			;
+	}
 }