kgdb,8250,pl011: Return immediately from console poll

The design of the kdb shell requires 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.

Changing the kernel debugger I/O API to require all polling character
routines to exit immediately if there is no data allows the kernel
debugger to process multiple input channels.

NO_POLL_CHAR will be the return code to the polling routine when ever
there is no character available.

CC: linux-serial@vger.kernel.org
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

7 files changed, 50 insertions, 11 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 2b1ea3d4c4f4..891e1dd65f24 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1891,8 +1891,8 @@ 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 743ebf5f16da..eb4cb480b93e 100644
--- a/drivers/serial/amba-pl011.c
+++ b/drivers/serial/amba-pl011.c
@@ -342,9 +342,9 @@ 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 4d93790faec3..d72fa3908128 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 78dd1e7120a9..ad839963fa68 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 6e1fa829fdeb..1d71df66f3fa 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -882,6 +882,8 @@ 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 188203a19657..3c000490a7dd 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 f024c0c4b8c4..bf6e8270e957 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);
         /* zero out any offline cpu data */
         for_each_present_cpu(i) {
                 if (!cpu_online(i)) {
@@ -112,6 +121,7 @@ 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)) {