watchdog: sp805: Don't write 0 to the load value register.

At least on the Versatile Express' V2M, calling wdt_disable followed by
wdt_enable, for instance by running the following sequence:

  echo V > /dev/watchdog; echo V > /dev/watchdog

results in an immediate reset.  The wdt_disable function writes 0 to the
load register; while the watchdog interrupts are disabled at this point,
this special value is defined to trigger an interrupt immediately.  It
appears that in this instance, the reset happens when the interrupts
are subsequently enabled by wdt_enable.

Putting in a short delay after writing a new load value in wdt_enable
solves the issue, but it seems cleaner to simply never write 0 to the
load register at all: according to the hardware docs, writing 0 to the
control register suffices to stop the counter, and the write of 0 to
the load register is questionable anyway since this register resets to
0xffffffff.

Signed-off-by: Nick Bowler <nbowler@elliptictech.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/watchdog/sp805_wdt.c b/drivers/watchdog/sp805_wdt.c
index 0d80e08b6439331e726fa8fe1c9f3c13e2deb0a5..c1e099aa57f36845f1035bfc802545e3ba2c91c3 100644 (file)
--- a/drivers/watchdog/sp805_wdt.c
+++ b/drivers/watchdog/sp805_wdt.c
@@ -144,7 +144,6 @@ static void wdt_disable(void)
 
        writel(UNLOCK, wdt->base + WDTLOCK);
        writel(0, wdt->base + WDTCONTROL);
-       writel(0, wdt->base + WDTLOAD);
        writel(LOCK, wdt->base + WDTLOCK);
 
        spin_unlock(&wdt->lock);