target/openrisc: Support non-busy idle state using PMR SPR

The OpenRISC architecture has the Power Management Register (PMR)
special purpose register to manage cpu power states.  The interesting
modes are:

 * Doze Mode (DME) - Stop cpu except timer & pic - wake on interrupt
 * Sleep Mode (SME) - Stop cpu and all units - wake on interrupt
 * Suspend Model (SUME) - Stop cpu and all units - wake on reset

The linux kernel will set DME when idle.

This patch implements the PMR SPR and halts the qemu cpu when there is a
change to DME or SME.  This means that openrisc qemu in no longer peggs
a host cpu at 100%.

In order for this to work we need to kick the CPU when timers are
expired.  Update the cpu timer to kick the cpu upon each timer event.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/openrisc/cputimer.c b/hw/openrisc/cputimer.c
index a98c799de6..febc469170 100644
--- a/hw/openrisc/cputimer.c
+++ b/hw/openrisc/cputimer.c
@@ -61,6 +61,7 @@ void cpu_openrisc_timer_update(OpenRISCCPU *cpu)
     }
     next = now + (uint64_t)wait * TIMER_PERIOD;
     timer_mod(cpu->env.timer, next);
+    qemu_cpu_kick(CPU(cpu));
 }
 
 void cpu_openrisc_count_start(OpenRISCCPU *cpu)