[PATCH V3 1/2] powerpc/perf: Add support for caps under sysfs in powerpc

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

Add caps support under "/sys/bus/event_source/devices/<pmu>/"
for powerpc. This directory can be used to expose some of the
specific features that powerpc PMU supports to the user.
Example: pmu_name. The name of PMU registered will depend on
platform, say power9 or power10 or it could be Generic Compat
PMU.

Currently the only way to know which is the registered
PMU is from the dmesg logs. But clearing the dmesg will make it
difficult to know exact PMU backend used. And even extracting
from dmesg will be complicated, as we need  to parse the dmesg
logs and add filters for pmu name. Whereas by exposing it via
caps will make it easy as we just need to directly read it from
the sysfs.

Add a caps directory to /sys/bus/event_source/devices/cpu/
for power8, power9, power10 and generic compat PMU in respective
PMU driver code. Update the pmu_name file under caps folder
in core-book3s using "attr_update".

The information exposed currently:
 - pmu_name : Underlying PMU name from the driver

Example result with power9 pmu:

 # ls /sys/bus/event_source/devices/cpu/caps
pmu_name

 # cat /sys/bus/event_source/devices/cpu/caps/pmu_name
POWER9

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
Changelog:
 v2 -> v3:
 Removed the newline in sysfs_emit.

 v1 -> v2:
 Move the show function as generic in core-book3s
 and update show function using sysfs_emit and ppmu->name
 Added Documention for this ABI in patch 2.
 Notes: The caps directory is implemented in PMU for other
 architectures already. Reference commit for x86:
 commit b00233b53065 ("perf/x86: Export some PMU attributes in caps/ directory")

 arch/powerpc/perf/core-book3s.c        | 31 ++++++++++++++++++++++++++
 arch/powerpc/perf/generic-compat-pmu.c | 10 +++++++++
 arch/powerpc/perf/power10-pmu.c        | 10 +++++++++
 arch/powerpc/perf/power8-pmu.c         | 10 +++++++++
 arch/powerpc/perf/power9-pmu.c         | 10 +++++++++
 5 files changed, 71 insertions(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index b5b42cf0a703..80237fd07010 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2488,6 +2488,33 @@ static int power_pmu_prepare_cpu(unsigned int cpu)
 	return 0;
 }
 
+static ssize_t pmu_name_show(struct device *cdev,
+		struct device_attribute *attr,
+		char *buf)
+{
+	if (ppmu)
+		return sysfs_emit(buf, "%s", ppmu->name);
+
+	return 0;
+}
+
+static DEVICE_ATTR_RO(pmu_name);
+
+static struct attribute *pmu_caps_attrs[] = {
+	&dev_attr_pmu_name.attr,
+	NULL
+};
+
+static const struct attribute_group pmu_caps_group = {
+	.name  = "caps",
+	.attrs = pmu_caps_attrs,
+};
+
+static const struct attribute_group *pmu_caps_groups[] = {
+	&pmu_caps_group,
+	NULL,
+};
+
 int __init register_power_pmu(struct power_pmu *pmu)
 {
 	if (ppmu)
@@ -2498,6 +2525,10 @@ int __init register_power_pmu(struct power_pmu *pmu)
 		pmu->name);
 
 	power_pmu.attr_groups = ppmu->attr_groups;
+
+	if (ppmu->flags & PPMU_ARCH_207S)
+		power_pmu.attr_update = pmu_caps_groups;
+
 	power_pmu.capabilities |= (ppmu->capabilities & PERF_PMU_CAP_EXTENDED_REGS);
 
 #ifdef MSR_HV
diff --git a/arch/powerpc/perf/generic-compat-pmu.c b/arch/powerpc/perf/generic-compat-pmu.c
index f3db88aee4dd..817c69863038 100644
--- a/arch/powerpc/perf/generic-compat-pmu.c
+++ b/arch/powerpc/perf/generic-compat-pmu.c
@@ -151,9 +151,19 @@ static const struct attribute_group generic_compat_pmu_format_group = {
 	.attrs = generic_compat_pmu_format_attr,
 };
 
+static struct attribute *generic_compat_pmu_caps_attrs[] = {
+	NULL
+};
+
+static struct attribute_group generic_compat_pmu_caps_group = {
+	.name  = "caps",
+	.attrs = generic_compat_pmu_caps_attrs,
+};
+
 static const struct attribute_group *generic_compat_pmu_attr_groups[] = {
 	&generic_compat_pmu_format_group,
 	&generic_compat_pmu_events_group,
+	&generic_compat_pmu_caps_group,
 	NULL,
 };
 
diff --git a/arch/powerpc/perf/power10-pmu.c b/arch/powerpc/perf/power10-pmu.c
index c6d51e7093cf..d1adcd9f52e2 100644
--- a/arch/powerpc/perf/power10-pmu.c
+++ b/arch/powerpc/perf/power10-pmu.c
@@ -258,6 +258,15 @@ static const struct attribute_group power10_pmu_format_group = {
 	.attrs = power10_pmu_format_attr,
 };
 
+static struct attribute *power10_pmu_caps_attrs[] = {
+	NULL
+};
+
+static struct attribute_group power10_pmu_caps_group = {
+	.name  = "caps",
+	.attrs = power10_pmu_caps_attrs,
+};
+
 static const struct attribute_group *power10_pmu_attr_groups_dd1[] = {
 	&power10_pmu_format_group,
 	&power10_pmu_events_group_dd1,
@@ -267,6 +276,7 @@ static const struct attribute_group *power10_pmu_attr_groups_dd1[] = {
 static const struct attribute_group *power10_pmu_attr_groups[] = {
 	&power10_pmu_format_group,
 	&power10_pmu_events_group,
+	&power10_pmu_caps_group,
 	NULL,
 };
 
diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
index e37b1e714d2b..2518f5375d4a 100644
--- a/arch/powerpc/perf/power8-pmu.c
+++ b/arch/powerpc/perf/power8-pmu.c
@@ -187,9 +187,19 @@ static const struct attribute_group power8_pmu_events_group = {
 	.attrs = power8_events_attr,
 };
 
+static struct attribute *power8_pmu_caps_attrs[] = {
+	NULL
+};
+
+static struct attribute_group power8_pmu_caps_group = {
+	.name  = "caps",
+	.attrs = power8_pmu_caps_attrs,
+};
+
 static const struct attribute_group *power8_pmu_attr_groups[] = {
 	&isa207_pmu_format_group,
 	&power8_pmu_events_group,
+	&power8_pmu_caps_group,
 	NULL,
 };
 
diff --git a/arch/powerpc/perf/power9-pmu.c b/arch/powerpc/perf/power9-pmu.c
index c393e837648e..5c654ce1a417 100644
--- a/arch/powerpc/perf/power9-pmu.c
+++ b/arch/powerpc/perf/power9-pmu.c
@@ -258,9 +258,19 @@ static const struct attribute_group power9_pmu_format_group = {
 	.attrs = power9_pmu_format_attr,
 };
 
+static struct attribute *power9_pmu_caps_attrs[] = {
+	NULL
+};
+
+static struct attribute_group power9_pmu_caps_group = {
+	.name  = "caps",
+	.attrs = power9_pmu_caps_attrs,
+};
+
 static const struct attribute_group *power9_pmu_attr_groups[] = {
 	&power9_pmu_format_group,
 	&power9_pmu_events_group,
+	&power9_pmu_caps_group,
 	NULL,
 };
 
-- 
2.35.1