[Qemu-devel] Re: [PATCH 3/3] mips: Expire late timers when reading cp0_count

[Edgar E. Iglesias]

On Tue, Jan 18, 2011 at 12:29:42AM +0100, address@hidden wrote:
> From: Edgar E. Iglesias <address@hidden>
> 
> When reading cp0_count from a timer with a late trigger that should
> already have expired, expire it and raise the timer irq.
> 
> This makes it possible for guest code (e.g, Linux) that first read
> cp0_count, then compare it with cp0_compare and check for raised
> timer interrupt lines to run reliably.
> 
> Signed-off-by: Edgar E. Iglesias <address@hidden>

Sorry sent the wrong version of this one. It's supposed to be the
following:

commit 139330de404209528712fd703952c0b5ad4459a1
Author: Edgar E. Iglesias <address@hidden>
Date:   Tue Jan 18 00:12:22 2011 +0100

    mips: Expire late timers when reading cp0_count
    
    When reading cp0_count from a timer with a late trigger that should
    already have expired, expire it and raise the timer irq.
    
    This makes it possible for guest code (e.g, Linux) that first read
    cp0_count, then compare it with cp0_compare and check for raised
    timer interrupt lines to run reliably.
    
    Signed-off-by: Edgar E. Iglesias <address@hidden>

diff --git a/hw/mips_timer.c b/hw/mips_timer.c
index 8c32087..9c95f28 100644
--- a/hw/mips_timer.c
+++ b/hw/mips_timer.c
@@ -69,9 +69,17 @@ uint32_t cpu_mips_get_count (CPUState *env)
     if (env->CP0_Cause & (1 << CP0Ca_DC)) {
         return env->CP0_Count;
     } else {
+        uint64_t now;
+
+        now = qemu_get_clock(vm_clock);
+        if (qemu_timer_pending(env->timer)
+            && qemu_timer_expired(env->timer, now)) {
+            /* The timer has already expired.  */
+            cpu_mips_timer_expire(env);
+        }
+
         return env->CP0_Count +
-            (uint32_t)muldiv64(qemu_get_clock(vm_clock),
-                               TIMER_FREQ, get_ticks_per_sec());
+            (uint32_t)muldiv64(now, TIMER_FREQ, get_ticks_per_sec());
     }
 }