W1: ds2490.c simplify and fix ds_touch_bit

Simplify and fix ds_touch_bit.  If a device is attached in the middle of a
bus search the status register will return more than the default 16 bytes.
 The additional bytes indicate that it has detected a new device.  The way
ds_wait_status is coded, if it doesn't read 16 status bytes it returns an
error value.  ds_touch_bit then will detect that error and return an
error.  In that case it doesn't read the input buffer and returns
uninitialized data.  It doesn't stop there.  The next transaction will not
expect the extra byte in the input buffer and the short read will cause an
error and clear out both the old byte and new data in the input buffer.

Just ignore the value of ds_wait_status.  It is still required to wait
until ds2490 is again idle and there is data to read when ds_recv_data is
called.  This also removes the while loop.  None of the other commands
wait and verify that the issued command is in the status register.

Signed-off-by: David Fries <david@fries.net>
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 17 deletions

diff --git a/drivers/w1/masters/ds2490.c b/drivers/w1/masters/ds2490.c
index 1b632d5..c4ff70b2 100644
--- a/drivers/w1/masters/ds2490.c
+++ b/drivers/w1/masters/ds2490.c
@@ -490,28 +490,15 @@ static int ds_set_pullup(struct ds_device *dev, int delay)
 
 static int ds_touch_bit(struct ds_device *dev, u8 bit, u8 *tbit)
 {
-	int err, count;
+	int err;
 	struct ds_status st;
-	u16 value = (COMM_BIT_IO | COMM_IM) | ((bit) ? COMM_D : 0);
-	u16 cmd;
 
-	err = ds_send_control(dev, value, 0);
+	err = ds_send_control(dev, COMM_BIT_IO | COMM_IM | (bit ? COMM_D : 0),
+		0);
 	if (err)
 		return err;
 
-	count = 0;
-	do {
-		err = ds_wait_status(dev, &st);
-		if (err)
-			return err;
-
-		cmd = st.command0 | (st.command1 << 8);
-	} while (cmd != value && ++count < 10);
-
-	if (err < 0 || count >= 10) {
-		printk(KERN_ERR "Failed to obtain status.\n");
-		return -EINVAL;
-	}
+	ds_wait_status(dev, &st);
 
 	err = ds_recv_data(dev, tbit, sizeof(*tbit));
 	if (err < 0)