[PATCH 1/2] MIPS: add 8250/16550 serial early printk driver

[Yoichi Yuasa <yuasa@linux-mips.org>]

Signed-off-by: Yoichi Yuasa <yuasa@linux-mips.org>
---
 arch/mips/Kconfig.debug              |    8 ++++
 arch/mips/include/asm/setup.h        |    9 ++++
 arch/mips/kernel/Makefile            |    1 +
 arch/mips/kernel/early_printk_8250.c |   68 ++++++++++++++++++++++++++++++++++
 4 files changed, 86 insertions(+), 0 deletions(-)
 create mode 100644 arch/mips/kernel/early_printk_8250.c

diff --git a/arch/mips/Kconfig.debug b/arch/mips/Kconfig.debug
index 32a010d..f5d739c 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 50511aa..7395b7f 100644
--- a/arch/mips/include/asm/setup.h
+++ b/arch/mips/include/asm/setup.h
@@ -5,6 +5,15 @@
 
 #ifdef  __KERNEL__
 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
+
 #endif /* __KERNEL__ */
 
 #endif /* __SETUP_H */
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 9326af5..03fc037 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -93,6 +93,7 @@ obj-$(CONFIG_GPIO_TXX9)		+= gpio_txx9.o
 
 obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
+obj-$(CONFIG_EARLY_PRINTK_8250)	+= early_printk_8250.o
 
 CFLAGS_cpu-bugs64.o	= $(shell if $(CC) $(KBUILD_CFLAGS) -Wa,-mdaddi -c -o /dev/null -xc /dev/null >/dev/null 2>&1; then echo "-DHAVE_AS_SET_DADDI"; fi)
 
diff --git a/arch/mips/kernel/early_printk_8250.c b/arch/mips/kernel/early_printk_8250.c
new file mode 100644
index 0000000..6faf8fd
--- /dev/null
+++ b/arch/mips/kernel/early_printk_8250.c
@@ -0,0 +1,68 @@
+/*
+ *  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 unsigned long 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 = base;
+	serial8250_reg_shift = reg_shift;
+	serial8250_tx_timeout = timeout;
+}
+
+static inline u8 serial_in(int offset)
+{
+	return readb((void __iomem *)serial8250_base +
+		     (offset << serial8250_reg_shift));
+}
+
+static inline void serial_out(int offset, char value)
+{
+	writeb(value, (void __iomem *)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);
+}
-- 
1.6.6.1