perf/amd/ibs: Use ->is_visible callback for dynamic attributes

Currently, some attributes are added at build time whereas others
at boot time depending on IBS pmu capabilities. Instead, we can
just add all attribute groups at build time but hide individual
group at boot time using more appropriate ->is_visible() callback.

Also, struct perf_ibs has bunch of fields for pmu attributes which
just pass on the pointer, does not do anything else. Remove them.

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220509044914.1473-3-ravi.bangoria@amd.com

Author: Ravi Bangoria

arch/x86/events/amd/ibs.c

@@ -94,10 +94,6 @@ struct perf_ibs {
 	unsigned int			fetch_ignore_if_zero_rip : 1;
 	struct cpu_perf_ibs __percpu	*pcpu;
 
-	struct attribute		**format_attrs;
-	struct attribute_group		format_group;
-	const struct attribute_group	*attr_groups[2];
-
 	u64				(*get_count)(u64 config);
 };
 
@@ -528,16 +524,61 @@ static void perf_ibs_del(struct perf_event *event, int flags)
 
 static void perf_ibs_read(struct perf_event *event) { }
 
+/*
+ * We need to initialize with empty group if all attributes in the
+ * group are dynamic.
+ */
+static struct attribute *attrs_empty[] = {
+	NULL,
+};
+
+static struct attribute_group empty_format_group = {
+	.name = "format",
+	.attrs = attrs_empty,
+};
+
+static const struct attribute_group *empty_attr_groups[] = {
+	&empty_format_group,
+	NULL,
+};
+
 PMU_FORMAT_ATTR(rand_en,	"config:57");
 PMU_FORMAT_ATTR(cnt_ctl,	"config:19");
 
-static struct attribute *ibs_fetch_format_attrs[] = {
+static struct attribute *rand_en_attrs[] = {
 	&format_attr_rand_en.attr,
 	NULL,
 };
 
-static struct attribute *ibs_op_format_attrs[] = {
-	NULL,	/* &format_attr_cnt_ctl.attr if IBS_CAPS_OPCNT */
+static struct attribute_group group_rand_en = {
+	.name = "format",
+	.attrs = rand_en_attrs,
+};
+
+static const struct attribute_group *fetch_attr_groups[] = {
+	&group_rand_en,
+	NULL,
+};
+
+static umode_t
+cnt_ctl_is_visible(struct kobject *kobj, struct attribute *attr, int i)
+{
+	return ibs_caps & IBS_CAPS_OPCNT ? attr->mode : 0;
+}
+
+static struct attribute *cnt_ctl_attrs[] = {
+	&format_attr_cnt_ctl.attr,
+	NULL,
+};
+
+static struct attribute_group group_cnt_ctl = {
+	.name = "format",
+	.attrs = cnt_ctl_attrs,
+	.is_visible = cnt_ctl_is_visible,
+};
+
+static const struct attribute_group *op_attr_update[] = {
+	&group_cnt_ctl,
 	NULL,
 };
 
@@ -561,7 +602,6 @@ static struct perf_ibs perf_ibs_fetch = {
 	.max_period		= IBS_FETCH_MAX_CNT << 4,
 	.offset_mask		= { MSR_AMD64_IBSFETCH_REG_MASK },
 	.offset_max		= MSR_AMD64_IBSFETCH_REG_COUNT,
-	.format_attrs		= ibs_fetch_format_attrs,
 
 	.get_count		= get_ibs_fetch_count,
 };
@@ -587,7 +627,6 @@ static struct perf_ibs perf_ibs_op = {
 	.max_period		= IBS_OP_MAX_CNT << 4,
 	.offset_mask		= { MSR_AMD64_IBSOP_REG_MASK },
 	.offset_max		= MSR_AMD64_IBSOP_REG_COUNT,
-	.format_attrs		= ibs_op_format_attrs,
 
 	.get_count		= get_ibs_op_count,
 };
@@ -757,17 +796,6 @@ static __init int perf_ibs_pmu_init(struct perf_ibs *perf_ibs, char *name)
 
 	perf_ibs->pcpu = pcpu;
 
-	/* register attributes */
-	if (perf_ibs->format_attrs[0]) {
-		memset(&perf_ibs->format_group, 0, sizeof(perf_ibs->format_group));
-		perf_ibs->format_group.name	= "format";
-		perf_ibs->format_group.attrs	= perf_ibs->format_attrs;
-
-		memset(&perf_ibs->attr_groups, 0, sizeof(perf_ibs->attr_groups));
-		perf_ibs->attr_groups[0]	= &perf_ibs->format_group;
-		perf_ibs->pmu.attr_groups	= perf_ibs->attr_groups;
-	}
-
 	ret = perf_pmu_register(&perf_ibs->pmu, name, -1);
 	if (ret) {
 		perf_ibs->pcpu = NULL;
@@ -779,7 +807,6 @@ static __init int perf_ibs_pmu_init(struct perf_ibs *perf_ibs, char *name)
 
 static __init int perf_event_ibs_init(void)
 {
-	struct attribute **attr = ibs_op_format_attrs;
 	int ret;
 
 	/*
@@ -792,21 +819,24 @@ static __init int perf_event_ibs_init(void)
 	if (boot_cpu_data.x86 == 0x19 && boot_cpu_data.x86_model < 0x10)
 		perf_ibs_fetch.fetch_ignore_if_zero_rip = 1;
 
+	perf_ibs_fetch.pmu.attr_groups = fetch_attr_groups;
+
 	ret = perf_ibs_pmu_init(&perf_ibs_fetch, "ibs_fetch");
 	if (ret)
 		return ret;
 
-	if (ibs_caps & IBS_CAPS_OPCNT) {
+	if (ibs_caps & IBS_CAPS_OPCNT)
 		perf_ibs_op.config_mask |= IBS_OP_CNT_CTL;
-		*attr++ = &format_attr_cnt_ctl.attr;
-	}
 
 	if (ibs_caps & IBS_CAPS_OPCNTEXT) {
 		perf_ibs_op.max_period  |= IBS_OP_MAX_CNT_EXT_MASK;
 		perf_ibs_op.config_mask	|= IBS_OP_MAX_CNT_EXT_MASK;
 		perf_ibs_op.cnt_mask    |= IBS_OP_MAX_CNT_EXT_MASK;
 	}
 
+	perf_ibs_op.pmu.attr_groups = empty_attr_groups;
+	perf_ibs_op.pmu.attr_update = op_attr_update;
+
 	ret = perf_ibs_pmu_init(&perf_ibs_op, "ibs_op");
 	if (ret)
 		goto err_op;