[POWERPC] Fix off-by-one error in setting decrementer on Book E/4xx (v2)
The decrementer in Book E and 4xx processors interrupts on the
transition from 1 to 0, rather than on the 0 to -1 transition as on
64-bit server and 32-bit "classic" (6xx/7xx/7xxx) processors. At the
moment we subtract 1 from the count of how many decrementer ticks are
required before the next interrupt before putting it into the
decrementer, which is correct for server/classic processors, but could
possibly cause the interrupt to happen too early on Book E and 4xx if
the timebase/decrementer frequency is low.
This fixes the problem by making set_dec subtract 1 from the count for
server and classic processors, instead of having the callers subtract
1. Since set_dec already had a bunch of ifdefs to handle different
processor types, there is no net increase in ugliness. :)
Note that calling set_dec(0) may not generate an interrupt on some
processors. To make sure that decrementer_set_next_event always calls
set_dec with an interval of at least 1 tick, we set min_delta_ns of
the decrementer_clockevent to correspond to 2 ticks (2 rather than 1
to compensate for truncations in the conversions between ticks and
ns).
This also removes a redundant call to set the decrementer to
0x7fffffff - it was already set to that earlier in timer_interrupt.
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
index f058955..780f826 100644
--- a/include/asm-powerpc/time.h
+++ b/include/asm-powerpc/time.h
@@ -176,25 +176,31 @@
#endif
}
+/*
+ * Note: Book E and 4xx processors differ from other PowerPC processors
+ * in when the decrementer generates its interrupt: on the 1 to 0
+ * transition for Book E/4xx, but on the 0 to -1 transition for others.
+ */
static inline void set_dec(int val)
{
#if defined(CONFIG_40x)
mtspr(SPRN_PIT, val);
#elif defined(CONFIG_8xx_CPU6)
- set_dec_cpu6(val);
+ set_dec_cpu6(val - 1);
#else
+#ifndef CONFIG_BOOKE
+ --val;
+#endif
#ifdef CONFIG_PPC_ISERIES
- int cur_dec;
-
if (firmware_has_feature(FW_FEATURE_ISERIES) &&
get_lppaca()->shared_proc) {
get_lppaca()->virtual_decr = val;
- cur_dec = get_dec();
- if (cur_dec > val)
+ if (get_dec() > val)
HvCall_setVirtualDecr();
- } else
+ return;
+ }
#endif
- mtspr(SPRN_DEC, val);
+ mtspr(SPRN_DEC, val);
#endif /* not 40x or 8xx_CPU6 */
}