MIPS: Loongson1B: Improve early printk

- Determine serial port for early printk according to kernel command line.
  - Move to 8250/16550 serial early printk driver.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8023/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson1/Kconfig

@@ -16,6 +16,7 @@ config LOONGSON1_LS1B
 	select SYS_SUPPORTS_HIGHMEM
 	select SYS_SUPPORTS_MIPS16
 	select SYS_HAS_EARLY_PRINTK
+	select USE_GENERIC_EARLY_PRINTK_8250
 	select COMMON_CLK
 
 endchoice

arch/mips/loongson1/common/prom.c

@@ -57,6 +57,7 @@ void __init prom_init_cmdline(void)
 
 void __init prom_init(void)
 {
+	void __iomem *uart_base;
 	prom_argc = fw_arg0;
 	prom_argv = (char **)fw_arg1;
 	prom_envp = (char **)fw_arg2;
@@ -65,23 +66,18 @@ void __init prom_init(void)
 
 	memsize = env_or_default("memsize", DEFAULT_MEMSIZE);
 	highmemsize = env_or_default("highmemsize", 0x0);
+
+	if (strstr(arcs_cmdline, "console=ttyS3"))
+		uart_base = ioremap_nocache(LS1X_UART3_BASE, 0x0f);
+	else if (strstr(arcs_cmdline, "console=ttyS2"))
+		uart_base = ioremap_nocache(LS1X_UART2_BASE, 0x0f);
+	else if (strstr(arcs_cmdline, "console=ttyS1"))
+		uart_base = ioremap_nocache(LS1X_UART1_BASE, 0x0f);
+	else
+		uart_base = ioremap_nocache(LS1X_UART0_BASE, 0x0f);
+	setup_8250_early_printk_port((unsigned long)uart_base, 0, 0);
 }
 
 void __init prom_free_prom_memory(void)
 {
 }
-
-#define PORT(offset)	(u8 *)(KSEG1ADDR(LS1X_UART0_BASE + offset))
-
-void prom_putchar(char c)
-{
-	int timeout;
-
-	timeout = 1024;
-
-	while (((readb(PORT(UART_LSR)) & UART_LSR_THRE) == 0)
-			&& (timeout-- > 0))
-		;
-
-	writeb(c, PORT(UART_TX));
-}