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, 10 insertions, 0 deletions

diff --git a/target/openrisc/cpu.h b/target/openrisc/cpu.h
index 938ccc3..2721432 100644
--- a/target/openrisc/cpu.h
+++ b/target/openrisc/cpu.h
@@ -140,6 +140,15 @@ enum {
     IMMUCFGR_HTR = (1 << 11),
 };
 
+/* Power management register */
+enum {
+    PMR_SDF = (15 << 0),
+    PMR_DME = (1 << 4),
+    PMR_SME = (1 << 5),
+    PMR_DCGE = (1 << 6),
+    PMR_SUME = (1 << 7),
+};
+
 /* Float point control status register */
 enum {
     FPCSR_FPEE = 1,
@@ -284,6 +293,7 @@ typedef struct CPUOpenRISCState {
     uint32_t immucfgr;        /* IMMU configure register */
     uint32_t esr;             /* Exception supervisor register */
     uint32_t evbar;           /* Exception vector base address register */
+    uint32_t pmr;             /* Power Management Register */
     uint32_t fpcsr;           /* Float register */
     float_status fp_status;