commit 0dfe952dc5c2921488a1172407857d5bb81d17a4
author Roman Kapl <rka@sysgo.com> Mon Jan 09 12:23:38 2017 +0100
committer David Gibson <david@gibson.dropbear.id.au> Tue Jan 31 10:10:14 2017 +1100
tree 9f7f0dd45ef584991cd94e04135bae9e27e8eb81
parent 2a084dadcbc207b27d3efc9d6c05cafb72fc83f0

ppc: Prevent inifnite loop in decrementer auto-reload.

If the DECAR register is set to 0, QEMU tries to reload the decrementer with
zero in an inifinite loop. According to PPC documentation, the decrementer is
triggered on 1->0 transition, so avoid reloading the decrementer if if is
already zero.

The problem does not manifest under Linux, but it is valid to set DECAR to zero
(and may make sense as part of decrementer initialization when interrupts are
disabled).

Signed-off-by: Roman Kapl <rka@sysgo.com>
[dwg: Fixed style nit]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/ppc_booke.c

diff --git a/hw/ppc/ppc_booke.c b/hw/ppc/ppc_booke.c
index ab8d026..60baffa 100644
--- a/hw/ppc/ppc_booke.c
+++ b/hw/ppc/ppc_booke.c
@@ -198,8 +198,12 @@
     booke_update_irq(cpu);
 
     if (env->spr[SPR_BOOKE_TCR] & TCR_ARE) {
-        /* Auto Reload */
-        cpu_ppc_store_decr(env, env->spr[SPR_BOOKE_DECAR]);
+        /* Do not reload 0, it is already there. It would just trigger
+         * the timer again and lead to infinite loop */
+        if (env->spr[SPR_BOOKE_DECAR] != 0) {
+            /* Auto Reload */
+            cpu_ppc_store_decr(env, env->spr[SPR_BOOKE_DECAR]);
+        }
     }
 }