[Qemu-devel] [PATCH v3 1/9] i6300esb: remove muldiv64()

[Laurent Vivier <lvivier@redhat.com>]

Originally, timers were ticks based, and it made sense to
add ticks to current time to know when to trigger an alarm.

But since commit:

7447545 change all other clock references to use nanosecond resolution accessors

All timers use nanoseconds and we need to convert ticks to nanoseconds, by
doing something like:

    y = muldiv64(x, get_ticks_per_sec(), PCI_FREQUENCY)

where x is the number of device ticks and y the number of system ticks.

y is used as nanoseconds in timer functions,
it works because 1 tick is 1 nanosecond.
(get_ticks_per_sec() is 10^9)

But as PCI frequency is 33 MHz, we can also do:

    y = x * 30; /* 33 MHz PCI period is 30 ns */

Which is much more simple.

This implies a 33.333333 MHz PCI frequency,
but this is correct.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
v3: part of "PCI: remove muldiv64()"
 hw/watchdog/wdt_i6300esb.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/hw/watchdog/wdt_i6300esb.c b/hw/watchdog/wdt_i6300esb.c
index cfa2b1b..a91c8fd 100644
--- a/hw/watchdog/wdt_i6300esb.c
+++ b/hw/watchdog/wdt_i6300esb.c
@@ -129,14 +129,9 @@ static void i6300esb_restart_timer(I6300State *d, int stage)
     else
         timeout <<= 5;
 
-    /* Get the timeout in units of ticks_per_sec.
-     *
-     * ticks_per_sec is typically 10^9 == 0x3B9ACA00 (30 bits), with
-     * 20 bits of user supplied preload, and 15 bits of scale, the
-     * 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);
+    /* Get the timeout in nanoseconds. */
+
+    timeout = timeout * 30; /* on a PCI bus, 1 tick is 30 ns*/
 
     i6300esb_debug("stage %d, timeout %" PRIi64 "\n", d->stage, timeout);
 
-- 
2.1.0