[SRU][G/linux-oracle][PATCH 15/18] perf/arm-cmn: Fix PMU instance naming

[Khalid Elmously]

From: Robin Murphy <robin.murphy at arm.com>

BugLink: https://bugs.launchpad.net/bugs/1925421

Although it's neat to avoid the suffix for the typical case of a
single PMU, it means systems with multiple CMN instances end up with
inconsistent naming. I think it also breaks perf tool's "uncore alias"
logic if the common instance prefix is also the full name of one.

Avoid any surprises by not trying to be clever and simply numbering
every instance, even when it might technically prove redundant.

Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
Link: https://lore.kernel.org/r/649a2281233f193d59240b13ed91b57337c77b32.1611839564.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <will at kernel.org>
(cherry picked from commit 79d7c3dca99fa96033695ddf5d495b775a3a137b)
Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
---
 Documentation/admin-guide/perf/arm-cmn.rst |  2 +-
 drivers/perf/arm-cmn.c                     | 13 ++++---------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/perf/arm-cmn.rst b/Documentation/admin-guide/perf/arm-cmn.rst
index 0e4809346014..796e25b7027b 100644
--- a/Documentation/admin-guide/perf/arm-cmn.rst
+++ b/Documentation/admin-guide/perf/arm-cmn.rst
@@ -17,7 +17,7 @@ PMU events
 ----------
 
 The PMU driver registers a single PMU device for the whole interconnect,
-see /sys/bus/event_source/devices/arm_cmn. Multi-chip systems may link
+see /sys/bus/event_source/devices/arm_cmn_0. Multi-chip systems may link
 more than one CMN together via external CCIX links - in this situation,
 each mesh counts its own events entirely independently, and additional
 PMU devices will be named arm_cmn_{1..n}.
diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
index cf85596f55ea..25f3a5a0d3a0 100644
--- a/drivers/perf/arm-cmn.c
+++ b/drivers/perf/arm-cmn.c
@@ -1502,7 +1502,7 @@ static int arm_cmn_probe(struct platform_device *pdev)
 	struct arm_cmn *cmn;
 	const char *name;
 	static atomic_t id;
-	int err, rootnode, this_id;
+	int err, rootnode;
 
 	cmn = devm_kzalloc(&pdev->dev, sizeof(*cmn), GFP_KERNEL);
 	if (!cmn)
@@ -1549,14 +1549,9 @@ static int arm_cmn_probe(struct platform_device *pdev)
 		.cancel_txn = arm_cmn_end_txn,
 	};
 
-	this_id = atomic_fetch_inc(&id);
-	if (this_id == 0) {
-		name = "arm_cmn";
-	} else {
-		name = devm_kasprintf(cmn->dev, GFP_KERNEL, "arm_cmn_%d", this_id);
-		if (!name)
-			return -ENOMEM;
-	}
+	name = devm_kasprintf(cmn->dev, GFP_KERNEL, "arm_cmn_%d", atomic_fetch_inc(&id));
+	if (!name)
+		return -ENOMEM;
 
 	err = cpuhp_state_add_instance(arm_cmn_hp_state, &cmn->cpuhp_node);
 	if (err)
-- 
2.17.1