[PATCH v3 1/2] arm64: errata: Factor out broken AMU const counter cap

[Beata Michalska <beata.michalska@arm.com>]

Move the workaround from the erratum 2457168-specific cpucap to a generic
broken AMU constant-counter one. This keeps the existing Cortex-A510
handling unchanged while allowing other errata with similar AMU constant
counter issue to share the capability bit and call sites.

Cc: <stable@vger.kernel.org>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 arch/arm64/Kconfig             |  8 ++++++++
 arch/arm64/kernel/cpu_errata.c | 23 +++++++++++++++++------
 arch/arm64/kernel/cpufeature.c |  2 +-
 arch/arm64/kernel/topology.c   |  7 ++++---
 arch/arm64/tools/cpucaps       |  2 +-
 5 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b5a51b0ef9440..3b6c052d46a18 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1040,9 +1040,17 @@ config ARM64_ERRATUM_1902691
 
 	  If unsure, say Y.
 
+config ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT
+	bool
+	# Targeting errata affecting AMEVCNTR01, the AMU constant counter.
+	# On affected CPUs the counter may not increment at the expected rate,
+	# making it unreliable. As a result, AMU users should treat it as
+	# unavailable rather than relying on misleading counter values.
+
 config ARM64_ERRATUM_2457168
 	bool "Cortex-A510: 2457168: workaround for AMEVCNTR01 incrementing incorrectly"
 	depends on ARM64_AMU_EXTN
+	select ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT
 	default y
 	help
 	  This option adds the workaround for ARM Cortex-A510 erratum 2457168.
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 5db8f0619e4bc..f18683e56184b 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -381,6 +381,18 @@ static const struct arm64_cpu_capabilities arm64_repeat_tlbi_list[] = {
 };
 #endif
 
+#ifdef CONFIG_ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT
+static const struct arm64_cpu_capabilities arm64_repeat_amu_constcnt_list[] = {
+#ifdef CONFIG_ARM64_ERRATUM_2457168
+	{
+		/* Cortex-A510 r0p0-r1p1 */
+		CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1)
+	},
+#endif
+	{}
+};
+#endif /* CONFIG_ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT */
+
 #ifdef CONFIG_CAVIUM_ERRATUM_23154
 static const struct midr_range cavium_erratum_23154_cpus[] = {
 	MIDR_ALL_VERSIONS(MIDR_THUNDERX),
@@ -916,14 +928,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		ERRATA_MIDR_REV_RANGE(MIDR_CORTEX_A510, 0, 0, 2)
 	},
 #endif
-#ifdef CONFIG_ARM64_ERRATUM_2457168
+#ifdef CONFIG_ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT
 	{
-		.desc = "ARM erratum 2457168",
-		.capability = ARM64_WORKAROUND_2457168,
+		.desc = "Broken AMU AMEVCNTR01 (const counter)",
+		.capability = ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT,
 		.type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
-
-		/* Cortex-A510 r0p0-r1p1 */
-		CAP_MIDR_RANGE(MIDR_CORTEX_A510, 0, 0, 1, 1)
+		.matches = cpucap_multi_entry_cap_matches,
+		.match_list = arm64_repeat_amu_constcnt_list
 	},
 #endif
 #ifdef CONFIG_ARM64_ERRATUM_2038923
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 17b83a2518a8f..1569f84214763 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2064,7 +2064,7 @@ static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap)
 		cpumask_set_cpu(smp_processor_id(), &amu_cpus);
 
 		/* 0 reference values signal broken/disabled counters */
-		if (!this_cpu_has_cap(ARM64_WORKAROUND_2457168))
+		if (!this_cpu_has_cap(ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT))
 			update_freq_counters_refs();
 	}
 }
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index d28438f8b83f1..64588554e7f76 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -402,7 +402,7 @@ static void cpu_read_constcnt(void *val)
 	 * the counter is disabled. A return value of 0 at counter read is
 	 * properly handled as an error case by the users of the counter.
 	 */
-	*(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_2457168) ?
+	*(u64 *)val = this_cpu_has_cap(ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT) ?
 		      0UL : read_constcnt();
 }
 
@@ -463,8 +463,9 @@ static void amu_read_core_const_ctrs(void *val)
 
 	/*
 	 * cpu_read_constcnt() incurs slight latency due to the
-	 * ARM64_WORKAROUND_2457168 check. Read it first to minimize
-	 * the sampling skew between the const and core counters.
+	 * ARM64_WORKAROUND_BROKEN_AMU_CONSTCNT check.
+	 * Read it first to minimize the sampling skew between the const
+	 * and core counters.
 	 */
 	cpu_read_constcnt(&ctrs->constcnt);
 	cpu_read_corecnt(&ctrs->corecnt);
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 2775ba3359cfe..58b6c084f9f25 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -105,7 +105,6 @@ WORKAROUND_1902691
 WORKAROUND_2038923
 WORKAROUND_2064142
 WORKAROUND_2077057
-WORKAROUND_2457168
 WORKAROUND_2645198
 WORKAROUND_2658417
 WORKAROUND_4193714
@@ -132,3 +131,4 @@ WORKAROUND_REPEAT_TLBI_SYNC
 WORKAROUND_SPECULATIVE_AT
 WORKAROUND_SPECULATIVE_SSBS
 WORKAROUND_SPECULATIVE_UNPRIV_LOAD
+WORKAROUND_BROKEN_AMU_CONSTCNT
-- 
2.43.0