[Qemu-devel] [PATCH][TRIVIAL] i6300esb: fix timer overflow

[Laurent Vivier <lvivier@redhat.com>]

We use muldiv64() to compute the time to wait:

    timeout = muldiv64(get_ticks_per_sec(), timeout, 33000000);

but get_ticks_per_sec() is 10^9 (30 bit value) and timeout
is a 35 bit value.

Whereas muldiv64 is:

    uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)

So we loose 3 bits of timeout.

Swapping get_ticks_per_sec() and timeout fixes it.

We can also replace it by a multiplication by 30 ns,
but this changes PCI clock frequency from 33MHz to 33.333333MHz
and we need to do this on all the QEMU PCI devices (later...)

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/watchdog/wdt_i6300esb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/watchdog/wdt_i6300esb.c b/hw/watchdog/wdt_i6300esb.c
index cfa2b1b..3e07d44 100644
--- a/hw/watchdog/wdt_i6300esb.c
+++ b/hw/watchdog/wdt_i6300esb.c
@@ -136,7 +136,7 @@ static void i6300esb_restart_timer(I6300State *d, int stage)
      * multiply here can exceed 64-bits, before we divide by 33MHz, so
      * we use a higher-precision intermediate result.
      */
-    timeout = muldiv64(get_ticks_per_sec(), timeout, 33000000);
+    timeout = muldiv64(timeout, get_ticks_per_sec(), 33000000);
 
     i6300esb_debug("stage %d, timeout %" PRIi64 "\n", d->stage, timeout);
 
-- 
2.1.0