This is a note to let you know that I've just added the patch titled
perf/arm-cmn: Workaround AmpereOneX errata AC04_MESH_1 (incorrect child count)
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-arm-cmn-workaround-ampereonex-errata-ac04_mesh_.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8d24321b89f5a20c4e6da9f3bbf73d57b717fe7a
Author: Ilkka Koskinen <ilkka@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri Feb 9 17:11:09 2024 +0000
perf/arm-cmn: Workaround AmpereOneX errata AC04_MESH_1 (incorrect child count)
[ Upstream commit 50572064ec7109b00eef8880e905f55861c8b3de ]
AmpereOneX mesh implementation has a bug in HN-P nodes that makes them
report incorrect child count. The failing crosspoints report 8 children
while they only have two.
When the driver tries to access the inexistent child nodes, it believes it
has reached an invalid node type and probing fails. The workaround is to
ignore those incorrect child nodes and continue normally.
Signed-off-by: Ilkka Koskinen <ilkka@xxxxxxxxxxxxxxxxxxxxxx>
[ rm: rewrote simpler generalised version ]
Tested-by: Ilkka Koskinen <ilkka@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Link: https://lore.kernel.org/r/ce4b1442135fe03d0de41859b04b268c88c854a3.1707498577.git.robin.murphy@xxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
index 6404b17d3aeb0..2c684e49a6fc7 100644
--- a/drivers/perf/arm-cmn.c
+++ b/drivers/perf/arm-cmn.c
@@ -2301,6 +2301,17 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
dev_dbg(cmn->dev, "ignoring external node %llx\n", reg);
continue;
}
+ /*
+ * AmpereOneX erratum AC04_MESH_1 makes some XPs report a bogus
+ * child count larger than the number of valid child pointers.
+ * A child offset of 0 can only occur on CMN-600; otherwise it
+ * would imply the root node being its own grandchild, which
+ * we can safely dismiss in general.
+ */
+ if (reg == 0 && cmn->part != PART_CMN600) {
+ dev_dbg(cmn->dev, "bogus child pointer?\n");
+ continue;
+ }
arm_cmn_init_node_info(cmn, reg & CMN_CHILD_NODE_ADDR, dn);
