target-arm: Fix errors in writes to generic timer control registers

The code for handling writes to the generic timer control registers
had several bugs:
 * ISTATUS (bit 2) is read-only but we forced it to zero on any write
 * the check for "was IMASK (bit 1) toggled?" incorrectly used '&' where
   it should be '^'
 * the handling of IMASK was inverted: we should set the IRQ if
   ISTATUS is set and IMASK is clear, not if both are set

The combination of these bugs meant that when running a Linux guest
that uses the generic timers we would fairly quickly end up either
forgetting that the timer output should be asserted, or failing to
set the IRQ when the timer was unmasked. The result is that the guest
never gets any more timer interrupts.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1401803208-1281-1-git-send-email-peter.maydell@linaro.org
Cc: qemu-stable@nongnu.org
(cherry picked from commit d3afacc7269fee45d54d1501a46b51f12ea7bb15)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/target-arm/helper.c b/target-arm/helper.c
index c3e491006f9729e9f485bcd325f032131e3b504d..6e673178119cd482dfd1bbf6d33972dcb659dd3a 100644 (file)
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -859,16 +859,16 @@ static int gt_ctl_write(CPUARMState *env, const ARMCPRegInfo *ri,
     int timeridx = ri->crm & 1;
     uint32_t oldval = env->cp15.c14_timer[timeridx].ctl;
 
-    env->cp15.c14_timer[timeridx].ctl = value & 3;
+    env->cp15.c14_timer[timeridx].ctl = deposit64(oldval, 0, 2, value);
     if ((oldval ^ value) & 1) {
         /* Enable toggled */
         gt_recalc_timer(cpu, timeridx);
-    } else if ((oldval & value) & 2) {
+    } else if ((oldval ^ value) & 2) {
         /* IMASK toggled: don't need to recalculate,
          * just set the interrupt line based on ISTATUS
          */
         qemu_set_irq(cpu->gt_timer_outputs[timeridx],
-                     (oldval & 4) && (value & 2));
+                     (oldval & 4) && !(value & 2));
     }
     return 0;
 }