[RFC 3/3] powernv/cpuidle : Introduce capability for firmware-enabled-stop

[Abhishek Goel]

This patch introduces the capability for firmware to handle the stop
states instead. A bit is set based on the discovery of the feature
and correspondingly also the responsibility to handle the stop states.

If Kernel does not know about stop version, it can fallback to opal for
idle stop support if firmware-stop-supported property is present.

Earlier this patch was posted as part of this series :
https://lkml.org/lkml/2020/3/4/589

Signed-off-by: Pratik Rajesh Sampat <psampat@xxxxxxxxxxxxx>
Signed-off-by: Abhishek Goel <huntbag@xxxxxxxxxxxxxxxxxx>
---

 v1->v2: This patch is newly added in this series.

 arch/powerpc/include/asm/processor.h  |  1 +
 arch/powerpc/kernel/dt_cpu_ftrs.c     |  8 ++++++++
 arch/powerpc/platforms/powernv/idle.c | 27 ++++++++++++++++-----------
 3 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 66fa20476d0e..d5c6532b11ef 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -430,6 +430,7 @@ extern unsigned long cpuidle_disable;
 enum idle_boot_override {IDLE_NO_OVERRIDE = 0, IDLE_POWERSAVE_OFF};
 
 #define STOP_ENABLE		0x00000001
+#define FIRMWARE_STOP_ENABLE	0x00000010
 
 #define STOP_VERSION_P9       0x1
 
diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index db1a525e090d..ff4a87b79702 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -298,6 +298,13 @@ static int __init feat_enable_idle_stop(struct dt_cpu_feature *f)
 	return 1;
 }
 
+static int __init feat_enable_firmware_stop(struct dt_cpu_feature *f)
+{
+	stop_dep.cpuidle_prop |= FIRMWARE_STOP_ENABLE;
+
+	return 1;
+}
+
 static int __init feat_enable_mmu_hash(struct dt_cpu_feature *f)
 {
 	u64 lpcr;
@@ -592,6 +599,7 @@ static struct dt_cpu_feature_match __initdata
 	{"idle-nap", feat_enable_idle_nap, 0},
 	{"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
 	{"idle-stop", feat_enable_idle_stop, 0},
+	{"firmware-stop-supported", feat_enable_firmware_stop, 0},
 	{"machine-check-power8", feat_enable_mce_power8, 0},
 	{"performance-monitor-power8", feat_enable_pmu_power8, 0},
 	{"data-stream-control-register", feat_enable_dscr, CPU_FTR_DSCR},
diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 538f0842ac3f..0de5de81902e 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -633,16 +633,6 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
 	unsigned long mmcr0 = 0;
 	struct p9_sprs sprs = {}; /* avoid false used-uninitialised */
 	bool sprs_saved = false;
-	int rc = 0;
-
-	/*
-	 * Kernel takes decision whether to make OPAL call or not. This logic
-	 * will be combined with the logic for BE opal to take decision.
-	 */
-	if (firmware_stop_supported) {
-		rc = opal_cpu_idle(cpu_to_be64(__pa(&srr1)), (uint64_t) psscr);
-		goto out;
-	}
 
 	if (!(psscr & (PSSCR_EC|PSSCR_ESL))) {
 		/* EC=ESL=0 case */
@@ -835,6 +825,19 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
 	return srr1;
 }
 
+static unsigned long power9_firmware_idle_stop(unsigned long psscr, bool mmu_on)
+{
+	unsigned long srr1;
+	int rc;
+
+	rc = opal_cpu_idle(cpu_to_be64(__pa(&srr1)), (uint64_t) psscr);
+
+	if (mmu_on)
+		mtmsr(MSR_KERNEL);
+	return srr1;
+
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 static unsigned long power9_offline_stop(unsigned long psscr)
 {
@@ -1394,9 +1397,11 @@ static int __init pnv_init_idle_states(void)
 	    !(stop_dep.cpuidle_prop & STOP_ENABLE))
 		goto out;
 
-	/* Check for supported version in kernel */
+	/* Check for supported version in kernel or fallback to kernel*/
 	if (stop_dep.stop_version & STOP_VERSION_P9) {
 		stop_dep.idle_stop = power9_idle_stop;
+	} else if (stop_dep.cpuidle_prop & FIRMWARE_STOP_ENABLE) {
+		stop_dep.idle_stop = power9_firmware_idle_stop;
 	} else {
 		stop_dep.idle_stop = NULL;
 		goto out;
-- 
2.17.1