perf/amd/ibs: Advertise zen4_ibs_extensions as pmu capability attribute

PMU driver can advertise certain feature via capability attribute('caps'
sysfs directory) which can be consumed by userspace tools like perf. Add
zen4_ibs_extensions capability attribute for IBS pmus. This attribute
will be enabled when CPUID_Fn8000001B_EAX[11] is set.

With patch on Zen4:

  $ ls /sys/bus/event_source/devices/ibs_op/caps
  zen4_ibs_extensions

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220509044914.1473-5-ravi.bangoria@amd.com

arch/x86/events/amd/ibs.c

@@ -537,15 +537,22 @@ static struct attribute_group empty_format_group = {
 	.attrs = attrs_empty,
 };
 
+static struct attribute_group empty_caps_group = {
+	.name = "caps",
+	.attrs = attrs_empty,
+};
+
 static const struct attribute_group *empty_attr_groups[] = {
 	&empty_format_group,
+	&empty_caps_group,
 	NULL,
 };
 
 PMU_FORMAT_ATTR(rand_en,	"config:57");
 PMU_FORMAT_ATTR(cnt_ctl,	"config:19");
 PMU_EVENT_ATTR_STRING(l3missonly, fetch_l3missonly, "config:59");
 PMU_EVENT_ATTR_STRING(l3missonly, op_l3missonly, "config:16");
+PMU_EVENT_ATTR_STRING(zen4_ibs_extensions, zen4_ibs_extensions, "1");
 
 static umode_t
 zen4_ibs_extensions_is_visible(struct kobject *kobj, struct attribute *attr, int i)
@@ -563,6 +570,11 @@ static struct attribute *fetch_l3missonly_attrs[] = {
 	NULL,
 };
 
+static struct attribute *zen4_ibs_extensions_attrs[] = {
+	&zen4_ibs_extensions.attr.attr,
+	NULL,
+};
+
 static struct attribute_group group_rand_en = {
 	.name = "format",
 	.attrs = rand_en_attrs,
@@ -574,13 +586,21 @@ static struct attribute_group group_fetch_l3missonly = {
 	.is_visible = zen4_ibs_extensions_is_visible,
 };
 
+static struct attribute_group group_zen4_ibs_extensions = {
+	.name = "caps",
+	.attrs = zen4_ibs_extensions_attrs,
+	.is_visible = zen4_ibs_extensions_is_visible,
+};
+
 static const struct attribute_group *fetch_attr_groups[] = {
 	&group_rand_en,
+	&empty_caps_group,
 	NULL,
 };
 
 static const struct attribute_group *fetch_attr_update[] = {
 	&group_fetch_l3missonly,
+	&group_zen4_ibs_extensions,
 	NULL,
 };
 
@@ -615,6 +635,7 @@ static struct attribute_group group_op_l3missonly = {
 static const struct attribute_group *op_attr_update[] = {
 	&group_cnt_ctl,
 	&group_op_l3missonly,
+	&group_zen4_ibs_extensions,
 	NULL,
 };