[PATCH] SCX200_ACB: eliminate spurious timeout errors

While busy-waiting for completion, check the hardware after scheduling;
don't schedule and then immediately check the _timeout_.  If the yield()
took a long time (as it does on my OLPC prototype board when it's busy),
we'd report a timeout even though the hardware was now ready.

This fixes it, and also switches the yield() for a cond_resched() because
we don't actually want to be _that_ nice about it.  I see nice
tightly-packed SMBus transactions now, rather than waiting for milliseconds
between successive phases.

Actually, we shouldn't be busy-waiting here at all.  We should be using
interrupts.  That's an exercise for another day though.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Cc: Christer Weinigel <wingel@nano-system.com>
Cc: <Jordan.Crouse@amd.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/i2c/busses/scx200_acb.c b/drivers/i2c/busses/scx200_acb.c
index ced309f..eae9e81 100644
--- a/drivers/i2c/busses/scx200_acb.c
+++ b/drivers/i2c/busses/scx200_acb.c
@@ -232,7 +232,7 @@ static void scx200_acb_poll(struct scx200_acb_iface *iface)
 	unsigned long timeout;
 
 	timeout = jiffies + POLL_TIMEOUT;
-	while (time_before(jiffies, timeout)) {
+	while (1) {
 		status = inb(ACBST);
 
 		/* Reset the status register to avoid the hang */
@@ -242,7 +242,10 @@ static void scx200_acb_poll(struct scx200_acb_iface *iface)
 			scx200_acb_machine(iface, status);
 			return;
 		}
-		yield();
+		if (time_after(jiffies, timeout))
+			break;
+		cpu_relax();
+		cond_resched();
 	}
 
 	dev_err(&iface->adapter.dev, "timeout in state %s\n",