MIPS: Add 8250/16550 serial early printk driver

Signed-off-by: Yoichi Yuasa <yuasa@linux-mips.org>
Cc: linux-mips <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/947/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

4 files changed, 83 insertions, 0 deletions

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 37871f0de15e..b147e7038ff0 100644
--- a/arch/mips/Kconfig.debug
+++ b/arch/mips/Kconfig.debug
@@ -20,6 +20,14 @@ config EARLY_PRINTK
           doesn't cooperate with an X server. You should normally say N here,
           unless you want to debug such a crash.
 
+config EARLY_PRINTK_8250
+        bool "8250/16550 and compatible serial early printk driver"
+        depends on EARLY_PRINTK
+        default n
+        help
+          If you say Y here, it will be possible to use a 8250/16550 serial
+          port as the boot console.
+
 config CMDLINE_BOOL
         bool "Built-in kernel command line"
         default n
diff --git a/arch/mips/include/asm/setup.h b/arch/mips/include/asm/setup.h
index e26589ef36ee..d7bfdeba9e84 100644
--- a/arch/mips/include/asm/setup.h
+++ b/arch/mips/include/asm/setup.h
@@ -5,6 +5,14 @@
 
 extern void setup_early_printk(void);
 
+#ifdef CONFIG_EARLY_PRINTK_8250
+extern void setup_8250_early_printk_port(unsigned long base,
+        unsigned int reg_shift, unsigned int timeout);
+#else
+static inline void setup_8250_early_printk_port(unsigned long base,
+        unsigned int reg_shift, unsigned int timeout) {}
+#endif
+
 extern void set_handler(unsigned long offset, void *addr, unsigned long len);
 extern void set_uncached_handler(unsigned long offset, void *addr, unsigned long len);
 
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 423d871a946b..4bbece9b3eb4 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -84,6 +84,7 @@ obj-$(CONFIG_GPIO_TXX9)		+= gpio_txx9.o
 obj-$(CONFIG_KEXEC)             += machine_kexec.o relocate_kernel.o crash.o
 obj-$(CONFIG_CRASH_DUMP)        += crash_dump.o
 obj-$(CONFIG_EARLY_PRINTK)      += early_printk.o
+obj-$(CONFIG_EARLY_PRINTK_8250) += early_printk_8250.o
 obj-$(CONFIG_SPINLOCK_TEST)     += spinlock_test.o
 obj-$(CONFIG_MIPS_MACHINE)      += mips_machine.o
 
diff --git a/arch/mips/kernel/early_printk_8250.c b/arch/mips/kernel/early_printk_8250.c
new file mode 100644
index 000000000000..83cea3767556
--- /dev/null
+++ b/arch/mips/kernel/early_printk_8250.c
@@ -0,0 +1,66 @@
+/*
+ *  8250/16550-type serial ports prom_putchar()
+ *
+ *  Copyright (C) 2010  Yoichi Yuasa <yuasa@linux-mips.org>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+#include <linux/io.h>
+#include <linux/serial_core.h>
+#include <linux/serial_reg.h>
+
+static void __iomem *serial8250_base;
+static unsigned int serial8250_reg_shift;
+static unsigned int serial8250_tx_timeout;
+
+void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
+                                  unsigned int timeout)
+{
+        serial8250_base = (void __iomem *)base;
+        serial8250_reg_shift = reg_shift;
+        serial8250_tx_timeout = timeout;
+}
+
+static inline u8 serial_in(int offset)
+{
+        return readb(serial8250_base + (offset << serial8250_reg_shift));
+}
+
+static inline void serial_out(int offset, char value)
+{
+        writeb(value, serial8250_base + (offset << serial8250_reg_shift));
+}
+
+void prom_putchar(char c)
+{
+        unsigned int timeout;
+        int status, bits;
+
+        if (!serial8250_base)
+                return;
+
+        timeout = serial8250_tx_timeout;
+        bits = UART_LSR_TEMT | UART_LSR_THRE;
+
+        do {
+                status = serial_in(UART_LSR);
+
+                if (--timeout == 0)
+                        break;
+        } while ((status & bits) != bits);
+
+        if (timeout)
+                serial_out(UART_TX, c);
+}