microblaze: Support early console on uart16550

Early console support reuse setting from U-BOOT that's why
it is not necessary to setup baudrates, etc.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/Kconfig.debug

@@ -10,7 +10,7 @@ source "lib/Kconfig.debug"
 
 config EARLY_PRINTK
 	bool "Early printk function for kernel"
-	depends on SERIAL_UARTLITE_CONSOLE
+	depends on SERIAL_UARTLITE_CONSOLE || SERIAL_8250_CONSOLE
 	default n
 	help
 	  This option turns on/off early printk messages to console.

arch/microblaze/include/asm/prom.h

@@ -27,6 +27,7 @@
 
 /* Other Prototypes */
 extern int early_uartlite_console(void);
+extern int early_uart16550_console(void);
 
 #ifdef CONFIG_PCI
 /*

arch/microblaze/kernel/early_printk.c

@@ -65,6 +65,50 @@ static struct console early_serial_uartlite_console = {
 };
 #endif /* CONFIG_SERIAL_UARTLITE_CONSOLE */
 
+#ifdef CONFIG_SERIAL_8250_CONSOLE
+static void early_printk_uart16550_putc(char c)
+{
+	/*
+	 * Limit how many times we'll spin waiting for TX FIFO status.
+	 * This will prevent lockups if the base address is incorrectly
+	 * set, or any other issue on the UARTLITE.
+	 * This limit is pretty arbitrary, unless we are at about 10 baud
+	 * we'll never timeout on a working UART.
+	 */
+
+	#define UART_LSR_TEMT	0x40 /* Transmitter empty */
+	#define UART_LSR_THRE	0x20 /* Transmit-hold-register empty */
+	#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
+
+	unsigned retries = 10000;
+
+	while (--retries &&
+		!((in_be32(base_addr + 0x14) & BOTH_EMPTY) == BOTH_EMPTY))
+		;
+
+	if (retries)
+		out_be32(base_addr, c & 0xff);
+}
+
+static void early_printk_uart16550_write(struct console *unused,
+					const char *s, unsigned n)
+{
+	while (*s && n-- > 0) {
+		early_printk_uart16550_putc(*s);
+		if (*s == '\n')
+			early_printk_uart16550_putc('\r');
+		s++;
+	}
+}
+
+static struct console early_serial_uart16550_console = {
+	.name = "earlyser",
+	.write = early_printk_uart16550_write,
+	.flags = CON_PRINTBUFFER,
+	.index = -1,
+};
+#endif /* CONFIG_SERIAL_8250_CONSOLE */
+
 static struct console *early_console;
 
 void early_printk(const char *fmt, ...)
@@ -103,6 +147,25 @@ int __init setup_early_printk(char *opt)
 	}
 #endif /* CONFIG_SERIAL_UARTLITE_CONSOLE */
 
+#ifdef CONFIG_SERIAL_8250_CONSOLE
+	base_addr = early_uart16550_console();
+	base_addr &= ~3; /* clear register offset */
+	if (base_addr) {
+		early_console_initialized = 1;
+#ifdef CONFIG_MMU
+		early_console_reg_tlb_alloc(base_addr);
+#endif
+		early_console = &early_serial_uart16550_console;
+
+		early_printk("early_printk_console is enabled at 0x%08x\n",
+							base_addr);
+
+		/* register_console(early_console); */
+
+		return 0;
+	}
+#endif /* CONFIG_SERIAL_8250_CONSOLE */
+
 	return 1;
 }
 

arch/microblaze/kernel/prom.c

@@ -89,6 +89,40 @@ int __init early_uartlite_console(void)
 {
 	return of_scan_flat_dt(early_init_dt_scan_serial, NULL);
 }
+
+/* MS this is Microblaze specifig function */
+static int __init early_init_dt_scan_serial_full(unsigned long node,
+				const char *uname, int depth, void *data)
+{
+	unsigned long l;
+	char *p;
+	unsigned int addr;
+
+	pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);
+
+/* find all serial nodes */
+	if (strncmp(uname, "serial", 6) != 0)
+		return 0;
+
+	early_init_dt_check_for_initrd(node);
+
+/* find compatible node with uartlite */
+	p = of_get_flat_dt_prop(node, "compatible", &l);
+
+	if ((strncmp(p, "xlnx,xps-uart16550", 18) != 0) &&
+		(strncmp(p, "xlnx,axi-uart16550", 18) != 0))
+		return 0;
+
+	addr = *(u32 *)of_get_flat_dt_prop(node, "reg", &l);
+	addr += *(u32 *)of_get_flat_dt_prop(node, "reg-offset", &l);
+	return addr; /* return address */
+}
+
+/* this function is looking for early uartlite console - Microblaze specific */
+int __init early_uart16550_console(void)
+{
+	return of_scan_flat_dt(early_init_dt_scan_serial_full, NULL);
+}
 #endif
 
 void __init early_init_devtree(void *params)