Add SME vector length detect

- cpuinfo_get_max_arm_sme_length() returns svl vector length in bits
- Display length of SME vectors in isa-tool

SME may be enabled on cpus that do not have SVE

Author: fbarchard

include/cpuinfo.h

@@ -1700,6 +1700,7 @@ struct cpuinfo_arm_isa {
 	bool sme_b16b16;
 	bool sme_f16f16;
 	uint32_t svelen;
+	uint32_t smelen;
 #endif
 	bool rdm;
 	bool fp16arith;
@@ -2081,6 +2082,15 @@ static inline uint32_t cpuinfo_get_max_arm_sve_length(void) {
 #endif
 }
 
+// Function to get the max SME vector length on ARM CPU's which support SME.
+static inline uint32_t cpuinfo_get_max_arm_sme_length(void) {
+#if CPUINFO_ARCH_ARM64
+	return cpuinfo_isa.smelen * 8; // bytes * 8 = bit length(vector length)
+#else
+	return 0;
+#endif
+}
+
 static inline bool cpuinfo_has_arm_sme(void) {
 #if CPUINFO_ARCH_ARM64
 	return cpuinfo_isa.sme;

src/arm/linux/aarch64-isa.c

@@ -191,4 +191,22 @@ void cpuinfo_arm64_linux_decode_isa_from_proc_cpuinfo(
 		// Mask out the SVE vector length bits
 		isa->svelen = ret & PR_SVE_VL_LEN_MASK;
 	}
+
+#ifndef PR_SME_GET_VL
+#define PR_SME_GET_VL 64
+#endif
+
+#ifndef PR_SME_VL_LEN_MASK
+#define PR_SME_VL_LEN_MASK 0xffff
+#endif
+
+	ret = prctl(PR_SME_GET_VL);
+	if (ret < 0) {
+		cpuinfo_log_warning("No SME support on this machine");
+		isa->smelen = 0; // Assume no SME support if the call fails
+	} else {
+		// Mask out the SME vector length bits
+		isa->smelen = ret & PR_SME_VL_LEN_MASK;
+	}
 }
+

tools/isa-info.c

@@ -178,6 +178,7 @@ int main(int argc, char** argv) {
 
 	printf("ARM SVE Capabilities:\n");
 	printf("\tSVE max length: %d\n", cpuinfo_get_max_arm_sve_length());
+	printf("\tSME max length: %d\n", cpuinfo_get_max_arm_sme_length());
 
 	printf("Cryptography extensions:\n");
 	printf("\tAES: %s\n", cpuinfo_has_arm_aes() ? "yes" : "no");