The decrementer store function has logic that short-cuts the timer if a
very small value is stored (0, 1, or 2) and raises an interrupt
directly. There are two problem with this on BookE.
First is that BookE says a decrementer interrupt should not be raised
on a store of 0, only of a decrement from 1. Second is that raising
the irq directly will bypass the auto-reload logic in the booke decr
timer function, breaking autoreload when 1 or 2 is stored.
Fix this by removing that small-value special case. It makes this
tricky logic even more difficult to reason about, and it hardly matters
for performance.
Cc: sdicaro@DDCI.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
These were some booke decrementer corner case issues I saw, probably
a little less important than the first patch so could go later.
Thanks,
Nick
hw/ppc/ppc.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index d80b0adc6c..1b1220c423 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -811,11 +811,7 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t
*nextp,
}
/*
- * Going from 2 -> 1, 1 -> 0 or 0 -> -1 is the event to generate a DEC
- * interrupt.
- *
- * If we get a really small DEC value, we can assume that by the time we
- * handled it we should inject an interrupt already.
+ * Going from 1 -> 0 or 0 -> -1 is the event to generate a DEC interrupt.
*
* On MSB level based DEC implementations the MSB always means the
interrupt
* is pending, so raise it on those.
@@ -823,8 +819,7 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t
*nextp,
* On MSB edge based DEC implementations the MSB going from 0 -> 1
triggers
* an edge interrupt, so raise it here too.
*/
- if ((value < 3) ||
- ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && signed_value < 0) ||
+ if (((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && signed_value < 0) ||
((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && signed_value < 0
&& signed_decr >= 0)) {
(*raise_excp)(cpu);