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, 2 insertions, 0 deletions

diff --git a/target/openrisc/interrupt.c b/target/openrisc/interrupt.c
index 2c91fab380..3959671c59 100644
--- a/target/openrisc/interrupt.c
+++ b/target/openrisc/interrupt.c
@@ -60,6 +60,8 @@ void openrisc_cpu_do_interrupt(CPUState *cs)
     env->sr |= SR_SM;
     env->sr &= ~SR_IEE;
     env->sr &= ~SR_TEE;
+    env->pmr &= ~PMR_DME;
+    env->pmr &= ~PMR_SME;
     env->tlb->cpu_openrisc_map_address_data = &cpu_openrisc_get_phys_nommu;
     env->tlb->cpu_openrisc_map_address_code = &cpu_openrisc_get_phys_nommu;
     env->lock_addr = -1;