[PATCH] parport: daisy chain end detection fix

Daisy chain end detection failed at least with older daisy chain devices that
do not implement the last device signal.

Signed-off-by: Marko Kohtala <marko.kohtala@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 17 insertions, 10 deletions

diff --git a/drivers/parport/daisy.c b/drivers/parport/daisy.c
index 075c7eb5c85d..6915114b9536 100644
--- a/drivers/parport/daisy.c
+++ b/drivers/parport/daisy.c
@@ -436,7 +436,7 @@ static int select_port (struct parport *port)
 
 static int assign_addrs (struct parport *port)
 {
-        unsigned char s, last_dev;
+        unsigned char s;
         unsigned char daisy;
         int thisdev = numdevs;
         int detected;
@@ -472,10 +472,13 @@ static int assign_addrs (struct parport *port)
         }
 
         parport_write_data (port, 0x78); udelay (2);
-        last_dev = 0; /* We've just been speaking to a device, so we
-                         know there must be at least _one_ out there. */
+        s = parport_read_status (port);
 
-        for (daisy = 0; daisy < 4; daisy++) {
+        for (daisy = 0;
+             (s & (PARPORT_STATUS_PAPEROUT|PARPORT_STATUS_SELECT))
+                     == (PARPORT_STATUS_PAPEROUT|PARPORT_STATUS_SELECT)
+                     && daisy < 4;
+             ++daisy) {
                 parport_write_data (port, daisy);
                 udelay (2);
                 parport_frob_control (port,
@@ -485,14 +488,18 @@ static int assign_addrs (struct parport *port)
                 parport_frob_control (port, PARPORT_CONTROL_STROBE, 0);
                 udelay (1);
 
-                if (last_dev)
-                        /* No more devices. */
-                        break;
+                add_dev (numdevs++, port, daisy);
 
-                last_dev = !(parport_read_status (port)
-                             & PARPORT_STATUS_BUSY);
+                /* See if this device thought it was the last in the
+                 * chain. */
+                if (!(s & PARPORT_STATUS_BUSY))
+                        break;
 
-                add_dev (numdevs++, port, daisy);
+                /* We are seeing pass through status now. We see
+                   last_dev from next device or if last_dev does not
+                   work status lines from some non-daisy chain
+                   device. */
+                s = parport_read_status (port);
         }
 
         parport_write_data (port, 0xff); udelay (2);