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>

4 files changed, 99 insertions, 1 deletions

diff --git a/arch/microblaze/Kconfig.debug b/arch/microblaze/Kconfig.debug
index e6e5e0da28c..e66e25c4b0b 100644
--- a/arch/microblaze/Kconfig.debug
+++ b/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.
diff --git a/arch/microblaze/include/asm/prom.h b/arch/microblaze/include/asm/prom.h
index 101fa098f62..bdc38312ae4 100644
--- a/arch/microblaze/include/asm/prom.h
+++ b/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
 /*
diff --git a/arch/microblaze/kernel/early_printk.c b/arch/microblaze/kernel/early_printk.c
index 685a64e93ed..c3616a080eb 100644
--- a/arch/microblaze/kernel/early_printk.c
+++ b/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;
 }
 
diff --git a/arch/microblaze/kernel/prom.c b/arch/microblaze/kernel/prom.c
index 427b13b4740..608e5cf2e10 100644
--- a/arch/microblaze/kernel/prom.c
+++ b/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)