[Qemu-devel] [PATCH] i6300esb: correctly convert watchdog clock ticks into nanoseconds

[Laurent Vivier <lvivier@redhat.com>]

Originally, qemu_mod_timer() was using ticks to count time.
And i6300esb was converting internal clock ticks (33 MHz) to
QEMU timer ticks.

The timer has been changed by a script to use nanoseconds:

    7447545 change all other clock references to use
            nanosecond resolution accessors

As i6300esb takes nanoseconds, we don't need anymore to
multiply counter by get_ticks_per_sec()/33MHz, but instead
we must convert watchdog ticks into nanoseconds.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/watchdog/wdt_i6300esb.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/hw/watchdog/wdt_i6300esb.c b/hw/watchdog/wdt_i6300esb.c
index cfa2b1b..21119ab 100644
--- a/hw/watchdog/wdt_i6300esb.c
+++ b/hw/watchdog/wdt_i6300esb.c
@@ -124,19 +124,24 @@ static void i6300esb_restart_timer(I6300State *d, int stage)
     else
         timeout = d->timer2_preload;
 
-    if (d->clock_scale == CLOCK_SCALE_1KHZ)
+    /* convert timeout to 33Mhz clock ticks */
+    if (d->clock_scale == CLOCK_SCALE_1KHZ) {
+        /* The 20-bit Preload Value is loaded into bits 34:15 of the
+         * main down counter. [...] The approximate clock generated
+         * is 1 KHz, (Default)
+         */
         timeout <<= 15;
-    else
+    } else {
+        /* The 20-bit Preload Value is loaded into bits 24:5 of the
+         * main down counter. [...] The approximate clock generated
+         * is 1 MHz.
+         */
         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.
+    }
+    /* A 33 Mhz clock gives a 30 ns tick,
+     * convert timeout from ticks to ns
      */
-    timeout = muldiv64(get_ticks_per_sec(), timeout, 33000000);
+    timeout *= 30;
 
     i6300esb_debug("stage %d, timeout %" PRIi64 "\n", d->stage, timeout);
 
-- 
2.1.0