arm64: add support for the AMU extension v1

The activity monitors extension is an optional extension introduced
by the ARMv8.4 CPU architecture. This implements basic support for
version 1 of the activity monitors architecture, AMUv1.

This support includes:
- Extension detection on each CPU (boot, secondary, hotplugged)
- Register interface for AMU aarch64 registers
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -1517,6 +1517,33 @@ config ARM64_PTR_AUTH
 
 endmenu
 
+menu "ARMv8.4 architectural features"
+
+config ARM64_AMU_EXTN
+	bool "Enable support for the Activity Monitors Unit CPU extension"
+	default y
+	help
+	  The activity monitors extension is an optional extension introduced
+	  by the ARMv8.4 CPU architecture. This enables support for version 1
+	  of the activity monitors architecture, AMUv1.
+
+	  To enable the use of this extension on CPUs that implement it, say Y.
+
+	  Note that for architectural reasons, firmware _must_ implement AMU
+	  support when running on CPUs that present the activity monitors
+	  extension. The required support is present in:
+	    * Version 1.5 and later of the ARM Trusted Firmware
+
+	  For kernels that have this configuration enabled but boot with broken
+	  firmware, you may need to say N here until the firmware is fixed.
+	  Otherwise you may experience firmware panics or lockups when
+	  accessing the counter registers. Even if you are not observing these
+	  symptoms, the values returned by the register reads might not
+	  correctly reflect reality. Most commonly, the value read will be 0,
+	  indicating that the counter is not enabled.
+
+endmenu
+
 menu "ARMv8.5 architectural features"
 
 config ARM64_E0PD

arch/arm64/include/asm/cpucaps.h

@@ -58,7 +58,8 @@
 #define ARM64_WORKAROUND_SPECULATIVE_AT_NVHE	48
 #define ARM64_HAS_E0PD				49
 #define ARM64_HAS_RNG				50
+#define ARM64_HAS_AMU_EXTN			51
 
-#define ARM64_NCAPS				51
+#define ARM64_NCAPS				52
 
 #endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/cpufeature.h

@@ -678,6 +678,11 @@ static inline bool cpu_has_hw_af(void)
 						ID_AA64MMFR1_HADBS_SHIFT);
 }
 
+#ifdef CONFIG_ARM64_AMU_EXTN
+/* Check whether the cpu supports the Activity Monitors Unit (AMU) */
+extern bool cpu_has_amu_feat(int cpu);
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif

arch/arm64/include/asm/sysreg.h

@@ -386,6 +386,42 @@
 #define SYS_TPIDR_EL0			sys_reg(3, 3, 13, 0, 2)
 #define SYS_TPIDRRO_EL0			sys_reg(3, 3, 13, 0, 3)
 
+/* Definitions for system register interface to AMU for ARMv8.4 onwards */
+#define SYS_AM_EL0(crm, op2)		sys_reg(3, 3, 13, (crm), (op2))
+#define SYS_AMCR_EL0			SYS_AM_EL0(2, 0)
+#define SYS_AMCFGR_EL0			SYS_AM_EL0(2, 1)
+#define SYS_AMCGCR_EL0			SYS_AM_EL0(2, 2)
+#define SYS_AMUSERENR_EL0		SYS_AM_EL0(2, 3)
+#define SYS_AMCNTENCLR0_EL0		SYS_AM_EL0(2, 4)
+#define SYS_AMCNTENSET0_EL0		SYS_AM_EL0(2, 5)
+#define SYS_AMCNTENCLR1_EL0		SYS_AM_EL0(3, 0)
+#define SYS_AMCNTENSET1_EL0		SYS_AM_EL0(3, 1)
+
+/*
+ * Group 0 of activity monitors (architected):
+ *                op0  op1  CRn   CRm       op2
+ * Counter:       11   011  1101  010:n<3>  n<2:0>
+ * Type:          11   011  1101  011:n<3>  n<2:0>
+ * n: 0-15
+ *
+ * Group 1 of activity monitors (auxiliary):
+ *                op0  op1  CRn   CRm       op2
+ * Counter:       11   011  1101  110:n<3>  n<2:0>
+ * Type:          11   011  1101  111:n<3>  n<2:0>
+ * n: 0-15
+ */
+
+#define SYS_AMEVCNTR0_EL0(n)		SYS_AM_EL0(4 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVTYPE0_EL0(n)		SYS_AM_EL0(6 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVCNTR1_EL0(n)		SYS_AM_EL0(12 + ((n) >> 3), (n) & 7)
+#define SYS_AMEVTYPE1_EL0(n)		SYS_AM_EL0(14 + ((n) >> 3), (n) & 7)
+
+/* AMU v1: Fixed (architecturally defined) activity monitors */
+#define SYS_AMEVCNTR0_CORE_EL0		SYS_AMEVCNTR0_EL0(0)
+#define SYS_AMEVCNTR0_CONST_EL0		SYS_AMEVCNTR0_EL0(1)
+#define SYS_AMEVCNTR0_INST_RET_EL0	SYS_AMEVCNTR0_EL0(2)
+#define SYS_AMEVCNTR0_MEM_STALL		SYS_AMEVCNTR0_EL0(3)
+
 #define SYS_CNTFRQ_EL0			sys_reg(3, 3, 14, 0, 0)
 
 #define SYS_CNTP_TVAL_EL0		sys_reg(3, 3, 14, 2, 0)
@@ -598,6 +634,7 @@
 #define ID_AA64PFR0_CSV3_SHIFT		60
 #define ID_AA64PFR0_CSV2_SHIFT		56
 #define ID_AA64PFR0_DIT_SHIFT		48
+#define ID_AA64PFR0_AMU_SHIFT		44
 #define ID_AA64PFR0_SVE_SHIFT		32
 #define ID_AA64PFR0_RAS_SHIFT		28
 #define ID_AA64PFR0_GIC_SHIFT		24
@@ -608,6 +645,7 @@
 #define ID_AA64PFR0_EL1_SHIFT		4
 #define ID_AA64PFR0_EL0_SHIFT		0
 
+#define ID_AA64PFR0_AMU			0x1
 #define ID_AA64PFR0_SVE			0x1
 #define ID_AA64PFR0_RAS_V1		0x1
 #define ID_AA64PFR0_FP_NI		0xf

arch/arm64/kernel/cpufeature.c

@@ -163,6 +163,7 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV2_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_DIT_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_AMU_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
 				   FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_SVE_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_RAS_SHIFT, 4, 0),
@@ -1222,6 +1223,53 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap,
 
 #endif
 
+#ifdef CONFIG_ARM64_AMU_EXTN
+
+/*
+ * The "amu_cpus" cpumask only signals that the CPU implementation for the
+ * flagged CPUs supports the Activity Monitors Unit (AMU) but does not provide
+ * information regarding all the events that it supports. When a CPU bit is
+ * set in the cpumask, the user of this feature can only rely on the presence
+ * of the 4 fixed counters for that CPU. But this does not guarantee that the
+ * counters are enabled or access to these counters is enabled by code
+ * executed at higher exception levels (firmware).
+ */
+static struct cpumask amu_cpus __read_mostly;
+
+bool cpu_has_amu_feat(int cpu)
+{
+	return cpumask_test_cpu(cpu, &amu_cpus);
+}
+
+static void cpu_amu_enable(struct arm64_cpu_capabilities const *cap)
+{
+	if (has_cpuid_feature(cap, SCOPE_LOCAL_CPU)) {
+		pr_info("detected CPU%d: Activity Monitors Unit (AMU)\n",
+			smp_processor_id());
+		cpumask_set_cpu(smp_processor_id(), &amu_cpus);
+	}
+}
+
+static bool has_amu(const struct arm64_cpu_capabilities *cap,
+		    int __unused)
+{
+	/*
+	 * The AMU extension is a non-conflicting feature: the kernel can
+	 * safely run a mix of CPUs with and without support for the
+	 * activity monitors extension. Therefore, unconditionally enable
+	 * the capability to allow any late CPU to use the feature.
+	 *
+	 * With this feature unconditionally enabled, the cpu_enable
+	 * function will be called for all CPUs that match the criteria,
+	 * including secondary and hotplugged, marking this feature as
+	 * present on that respective CPU. The enable function will also
+	 * print a detection message.
+	 */
+
+	return true;
+}
+#endif
+
 #ifdef CONFIG_ARM64_VHE
 static bool runs_at_el2(const struct arm64_cpu_capabilities *entry, int __unused)
 {
@@ -1499,6 +1547,24 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.cpu_enable = cpu_clear_disr,
 	},
 #endif /* CONFIG_ARM64_RAS_EXTN */
+#ifdef CONFIG_ARM64_AMU_EXTN
+	{
+		/*
+		 * The feature is enabled by default if CONFIG_ARM64_AMU_EXTN=y.
+		 * Therefore, don't provide .desc as we don't want the detection
+		 * message to be shown until at least one CPU is detected to
+		 * support the feature.
+		 */
+		.capability = ARM64_HAS_AMU_EXTN,
+		.type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
+		.matches = has_amu,
+		.sys_reg = SYS_ID_AA64PFR0_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64PFR0_AMU_SHIFT,
+		.min_field_value = ID_AA64PFR0_AMU,
+		.cpu_enable = cpu_amu_enable,
+	},
+#endif /* CONFIG_ARM64_AMU_EXTN */
 	{
 		.desc = "Data cache clean to the PoU not required for I/D coherence",
 		.capability = ARM64_HAS_CACHE_IDC,