powerpc/powernv: Save/Restore additional SPRs for stop4 cpuidle

The stop4 idle state on POWER9 is a deep idle state which loses
hypervisor resources, but whose latency is low enough that it can be
exposed via cpuidle.

Until now, the deep idle states which lose hypervisor resources (eg:
winkle) were only exposed via CPU-Hotplug.  Hence currently on wakeup
from such states, barring a few SPRs which need to be restored to
their older value, rest of the SPRS are reinitialized to their values
corresponding to that at boot time.

When stop4 is used in the context of cpuidle, we want these additional
SPRs to be restored to their older value, to ensure that the context
on the CPU coming back from idle is same as it was before going idle.

In this patch, we define a SPR save area in PACA (since we have used
up the volatile register space in the stack) and on POWER9, we restore
SPRN_PID, SPRN_LDBAR, SPRN_FSCR, SPRN_HFSCR, SPRN_MMCRA, SPRN_MMCR1,
SPRN_MMCR2 to the values they had before entering stop.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index dc88a31cc79a..04b60af027ae 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -31,6 +31,7 @@
 #endif
 #include <asm/accounting.h>
 #include <asm/hmi.h>
+#include <asm/cpuidle.h>
 
 register struct paca_struct *local_paca asm("r13");
 
@@ -183,6 +184,12 @@ struct paca_struct {
 	struct paca_struct **thread_sibling_pacas;
 	/* The PSSCR value that the kernel requested before going to stop */
 	u64 requested_psscr;
+
+	/*
+	 * Save area for additional SPRs that need to be
+	 * saved/restored during cpuidle stop.
+	 */
+	struct stop_sprs stop_sprs;
 #endif
 
 #ifdef CONFIG_PPC_STD_MMU_64