[PATCH] ARM: 2701/1: free up ixp2000 timer 4 for the watchdog

Patch from Lennert Buytenhek

The IXP2000 has four timers, but if we're on an A-step IXP2800, timer
2 and 3 don't work.  We need two timers for timekeeping (one for the
timer interrupt and one for tracking missed jiffies), so on early
IXP2800s we have no other choice but to use timer 1 and 4 for that,
but on all other IXP2000s we'd rather leave timer 4 free since that's
the only timer we can use for the watchdog.
So, on buggy IXP2000s (i.e. the A-step IXP2800) we use timer 4 for
tracking missed jiffies, and on all all non-buggy IXP2000s (i.e.
everything but the A-step IXP2800) we use timer 2.
On a pre-production IXP2800, this patch should print these messages
on boot:
	Enabling IXP2800 erratum #25 workaround
	Unable to use IXP2000 watchdog due to IXP2800 erratum #25
On any non-buggy IXP2800 (as well as on IXP2400s) you shouldn't see
anything at all, and the watchdog should be usable again.

Signed-off-by: Lennert Buytenhek
Signed-off-by: Deepak Saxena
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/char/watchdog/ixp2000_wdt.c b/drivers/char/watchdog/ixp2000_wdt.c
index ab659d37b4d2..4e98c215e5b1 100644
--- a/drivers/char/watchdog/ixp2000_wdt.c
+++ b/drivers/char/watchdog/ixp2000_wdt.c
@@ -192,7 +192,12 @@ static struct miscdevice ixp2000_wdt_miscdev =
 
 static int __init ixp2000_wdt_init(void)
 {
-	wdt_tick_rate = (*IXP2000_T1_CLD * HZ)/ 256;;
+	if ((*IXP2000_PRODUCT_ID & 0x001ffef0) == 0x00000000) {
+		printk(KERN_INFO "Unable to use IXP2000 watchdog due to IXP2800 erratum #25.\n");
+		return -EIO;
+	}
+
+	wdt_tick_rate = (*IXP2000_T1_CLD * HZ) / 256;
 
 	return misc_register(&ixp2000_wdt_miscdev);
 }