[RFC] Support stop state version quirk and firmware enabled stop

[Pratik Rajesh Sampat <psampat@linux.ibm.com>]

A concept patch in Skiboot to illustrate the case wherein handling of
stop states for different DD versions of a CPU can be achieved by a
simple modification in the list of cpu_features.
As an example idle-stop1 is defined which uses P9_CPU_DD1 to define the
cpu feature.

Along with that, an implementation is being worked upon the LE OPAL
series which helps OPAL handle the stop state entry and exit.

This patch advertises this capability of the firmware which can be
availed if the quirk-version-setting is not cognizable.

The firmware-enabled stop is being worked by Abhishek Goel
<huntbag@linux.vnet.ibm.com> building upon the LE OPAL series.

Signed-off-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
---
 core/cpufeatures.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/core/cpufeatures.c b/core/cpufeatures.c
index ec30c975..b9875e7b 100644
--- a/core/cpufeatures.c
+++ b/core/cpufeatures.c
@@ -510,6 +510,25 @@ static const struct cpu_feature cpu_features_table[] = {
 	-1, -1, -1,
 	NULL, },
 
+	/*
+	 * QUIRK for ISAv3.0B stop idle instructions and registers
+	 * Helps us determine if there are any quirks
+	 * XXX: Same of idle-stop
+	 */
+	{ "idle-stop-v1",
+	CPU_P9_DD1,
+	ISA_V3_0B, USABLE_HV|USABLE_OS,
+	HV_CUSTOM, OS_CUSTOM,
+	-1, -1, -1,
+	NULL, },
+
+	{ "firmware-stop-supported",
+	CPU_P9,
+	ISA_V3_0B, USABLE_HV|USABLE_OS,
+	HV_CUSTOM, OS_CUSTOM,
+	-1, -1, -1,
+	NULL, },
+
 	/*
 	 * ISAv3.0B Hypervisor Virtualization Interrupt
 	 * Also associated system registers, LPCR EE, HEIC, HVICE,
@@ -883,6 +902,9 @@ static void add_cpufeatures(struct dt_node *cpus,
 		const struct cpu_feature *f = &cpu_features_table[i];
 
 		if (f->cpus_supported & cpu_feature_cpu) {
+			if (!strcmp(f->name, "firmware-stop-supported") &&
+			    HAVE_BIG_ENDIAN)
+				continue;
 			DBG("  '%s'\n", f->name);
 			add_cpu_feature_nodeps(features, f);
 		}
-- 
2.24.1