[PATCH V2] perf/x86/uncore: Correct the number of CHAs on EMR

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Starting from SPR, the basic uncore PMON information is retrieved from
the discovery table (resides in an MMIO space populated by BIOS). It is
called the discovery method. The existing value of the type->num_boxes
is from the discovery table.

On some SPR variants, there is a firmware bug. So the value from the
discovery table is incorrect. We use the value from the
SPR_MSR_UNC_CBO_CONFIG to replace the one from the discovery table.
Commit 38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR")

Unfortunately, the SPR_MSR_UNC_CBO_CONFIG isn't available for the EMR
XCC (Always returns 0). But the above firmware bug
doesn't impact the EMR XCC. Don't let the value from the MSR replace
the existing value from the discovery table.

Fixes: 38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR")
Reported-by: Stephane Eranian <eranian@xxxxxxxxxx>
Reported-by: Yunying Sun <yunying.sun@xxxxxxxxx>
Tested-by: Yunying Sun <yunying.sun@xxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
 arch/x86/events/intel/uncore_snbep.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
index 4d349986f76a..8250f0f59c2b 100644
--- a/arch/x86/events/intel/uncore_snbep.c
+++ b/arch/x86/events/intel/uncore_snbep.c
@@ -6474,8 +6474,18 @@ void spr_uncore_cpu_init(void)
 
 	type = uncore_find_type_by_id(uncore_msr_uncores, UNCORE_SPR_CHA);
 	if (type) {
+		/*
+		 * The value from the discovery table (stored in the type->num_boxes
+		 * of UNCORE_SPR_CHA) is incorrect on some SPR variants because of a
+		 * firmware bug. Using the value from SPR_MSR_UNC_CBO_CONFIG to replace it.
+		 */
 		rdmsrl(SPR_MSR_UNC_CBO_CONFIG, num_cbo);
-		type->num_boxes = num_cbo;
+		/*
+		 * The MSR doesn't work on the EMR XCC, but the firmware bug doesn't impact
+		 * the EMR XCC. Don't let the value from the MSR replace the existing value.
+		 */
+		if (num_cbo)
+			type->num_boxes = num_cbo;
 	}
 	spr_uncore_iio_free_running.num_boxes = uncore_type_max_boxes(uncore_msr_uncores, UNCORE_SPR_IIO);
 }
-- 
2.35.1