[PATCH 12/40] kgdb,8250,pl011: Return immediately from console poll

[Jason Wessel <jason.wessel@windriver.com>]

The design of kdb required that every device that can provide input to
kdb have a polling routine that exits immediately if there is no
character available.

This is required in order to get the page scrolling mechanism working,
it is also a reasonable requirement for future kgdb I/O drivers
because that allows for the possibility of multiple input channels.

NO_POLL_CHAR will be the return code to the polling routine when ever
there is no character available.  There are several other console
polling drivers which can be modified, but for the prototype only the
8250 and pl011 driver have been changed to make use of this.

CC: linux-serial@vger.kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 drivers/serial/8250.c           |    4 ++--
 drivers/serial/amba-pl011.c     |    6 +++---
 include/linux/kdb.h             |    1 +
 include/linux/serial_core.h     |    1 +
 kernel/debug/debug_core.c       |    2 ++
 kernel/debug/gdbstub.c          |   37 +++++++++++++++++++++++++++++++------
 kernel/debug/kdb/kdb_debugger.c |   10 ++++++++++
 7 files changed, 50 insertions(+), 11 deletions(-)

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index c3e37c8..a488c60 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1895,8 +1895,8 @@ static int serial8250_get_poll_char(struct uart_port *port)
 	struct uart_8250_port *up = (struct uart_8250_port *)port;
 	unsigned char lsr = serial_inp(up, UART_LSR);
 
-	while (!(lsr & UART_LSR_DR))
-		lsr = serial_inp(up, UART_LSR);
+	if (!(lsr & UART_LSR_DR))
+		return NO_POLL_CHAR;
 
 	return serial_inp(up, UART_RX);
 }
diff --git a/drivers/serial/amba-pl011.c b/drivers/serial/amba-pl011.c
index ef7adc8..b411115 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -335,9 +335,9 @@ static int pl010_get_poll_char(struct uart_port *port)
 	struct uart_amba_port *uap = (struct uart_amba_port *)port;
 	unsigned int status;
 
-	do {
-		status = readw(uap->port.membase + UART01x_FR);
-	} while (status & UART01x_FR_RXFE);
+	status = readw(uap->port.membase + UART01x_FR);
+	if (status & UART01x_FR_RXFE)
+		return NO_POLL_CHAR;
 
 	return readw(uap->port.membase + UART01x_DR);
 }
diff --git a/include/linux/kdb.h b/include/linux/kdb.h
index d7fc145..bff071e 100644
--- a/include/linux/kdb.h
+++ b/include/linux/kdb.h
@@ -19,6 +19,7 @@
 #include <asm/atomic.h>
 
 #define KDB_POLL_FUNC_MAX	5
+extern int kdb_poll_idx;
 
 /*
  * kdb_initial_cpu is initialized to -1, and is set to the cpu
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 8c3dd36..d40db83 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -246,6 +246,7 @@ struct uart_ops {
 #endif
 };
 
+#define NO_POLL_CHAR		0x00ff0000
 #define UART_CONFIG_TYPE	(1 << 0)
 #define UART_CONFIG_IRQ		(1 << 1)
 
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index f1bc63b..4a90148 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -869,6 +869,8 @@ EXPORT_SYMBOL_GPL(kgdb_unregister_io_module);
 int dbg_io_get_char(void)
 {
 	int ret = dbg_io_ops->read_char();
+	if (ret == NO_POLL_CHAR)
+		return -1;
 	if (!dbg_kdb_mode)
 		return ret;
 	if (ret == 127)
diff --git a/kernel/debug/gdbstub.c b/kernel/debug/gdbstub.c
index 195ffbd..6965b5c 100644
--- a/kernel/debug/gdbstub.c
+++ b/kernel/debug/gdbstub.c
@@ -30,6 +30,7 @@
 
 #include <linux/kernel.h>
 #include <linux/kgdb.h>
+#include <linux/kdb.h>
 #include <linux/reboot.h>
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
@@ -62,6 +63,30 @@ static int hex(char ch)
 	return -1;
 }
 
+#ifdef CONFIG_KGDB_KDB
+static int gdbstub_read_wait(void)
+{
+	int ret = -1;
+	int i;
+
+	/* poll any additional I/O interfaces that are defined */
+	while (ret < 0)
+		for (i = 0; kdb_poll_funcs[i] != NULL; i++) {
+			ret = kdb_poll_funcs[i]();
+			if (ret > 0)
+				break;
+		}
+	return ret;
+}
+#else
+static int gdbstub_read_wait(void)
+{
+	int ret = dbg_io_ops->read_char();
+	while (ret == NO_POLL_CHAR)
+		ret = dbg_io_ops->read_char();
+	return ret;
+}
+#endif
 /* scan for the sequence $<data>#<checksum> */
 static void get_packet(char *buffer)
 {
@@ -75,7 +100,7 @@ static void get_packet(char *buffer)
 		 * Spin and wait around for the start character, ignore all
 		 * other characters:
 		 */
-		while ((ch = (dbg_io_ops->read_char())) != '$')
+		while ((ch = (gdbstub_read_wait())) != '$')
 			/* nothing */;
 
 		kgdb_connected = 1;
@@ -88,7 +113,7 @@ static void get_packet(char *buffer)
 		 * now, read until a # or end of buffer is found:
 		 */
 		while (count < (BUFMAX - 1)) {
-			ch = dbg_io_ops->read_char();
+			ch = gdbstub_read_wait();
 			if (ch == '#')
 				break;
 			checksum = checksum + ch;
@@ -98,8 +123,8 @@ static void get_packet(char *buffer)
 		buffer[count] = 0;
 
 		if (ch == '#') {
-			xmitcsum = hex(dbg_io_ops->read_char()) << 4;
-			xmitcsum += hex(dbg_io_ops->read_char());
+			xmitcsum = hex(gdbstub_read_wait()) << 4;
+			xmitcsum += hex(gdbstub_read_wait());
 
 			if (checksum != xmitcsum)
 				/* failed checksum */
@@ -144,10 +169,10 @@ static void put_packet(char *buffer)
 			dbg_io_ops->flush();
 
 		/* Now see what we get in reply. */
-		ch = dbg_io_ops->read_char();
+		ch = gdbstub_read_wait();
 
 		if (ch == 3)
-			ch = dbg_io_ops->read_char();
+			ch = gdbstub_read_wait();
 
 		/* If we get an ACK, we are done. */
 		if (ch == '+')
diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index 4cc5a69..966ea36 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -20,7 +20,15 @@
 get_char_func kdb_poll_funcs[] = {
 	dbg_io_get_char,
 	NULL,
+	NULL,
+	NULL,
+	NULL,
+	NULL,
 };
+EXPORT_SYMBOL_GPL(kdb_poll_funcs);
+
+int kdb_poll_idx = 1;
+EXPORT_SYMBOL_GPL(kdb_poll_idx);
 
 int kdb_stub(struct kgdb_state *ks)
 {
@@ -85,6 +93,7 @@ int kdb_stub(struct kgdb_state *ks)
 	kdb_bp_remove();
 	KDB_STATE_CLEAR(DOING_SS);
 	KDB_STATE_CLEAR(DOING_SSB);
+	KDB_STATE_SET(PAGER);
 	for_each_online_cpu(i) {
 		kdb_save_running_cpu(kgdb_info[i].debuggerinfo,
 				     kgdb_info[i].task, i);
@@ -108,6 +117,7 @@ int kdb_stub(struct kgdb_state *ks)
 	kdb_initial_cpu = -1;
 	kdb_current_task = NULL;
 	kdb_current_regs = NULL;
+	KDB_STATE_CLEAR(PAGER);
 	kdbnearsym_cleanup();
 	if (error == KDB_CMD_KGDB) {
 		if (KDB_STATE(DOING_KGDB) || KDB_STATE(DOING_KGDB2)) {
-- 
1.6.3.1.9.g95405b