perf arm-spe: Use old behavior when opening old SPE files

Since the linked commit, we stopped interpreting data source if the
perf.data file doesn't have the new metadata version. This means that
perf c2c will show no samples in this case.

Keep the old behavior so old files can be opened, but also still show
the new warning that updating might improve the decoding.

Also re-write the warning to be more concise and specific to a user.

Fixes: ba5e7169e548 ("perf arm-spe: Use metadata to decide the data source feature")
Signed-off-by: James Clark <[e-mail]>
Reviewed-by: Leo Yan <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Will Deacon <[e-mail]>
Cc: Mike Leach <[e-mail]>
Cc: [e-mail]
Cc: Besar Wicaksono <[e-mail]>
Cc: John Garry <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/arm-spe.c

···
 	u64 *metadata = NULL;
 	u64 midr = 0;
 
-	/*
-	 * Metadata version 1 doesn't contain any info for MIDR.
-	 * Simply return false in this case.
-	 */
+	/* Metadata version 1 assumes all CPUs are the same (old behavior) */
 	if (spe->metadata_ver == 1) {
-		pr_warning_once("The data file contains metadata version 1, "
-				"which is absent the info for data source. "
-				"Please upgrade the tool to record data.\n");
-		return false;
-	}
+		const char *cpuid;
 
-	/* CPU ID is -1 for per-thread mode */
-	if (speq->cpu < 0) {
-		/*
-		 * On the heterogeneous system, due to CPU ID is -1,
-		 * cannot confirm the data source packet is supported.
-		 */
-		if (!spe->is_homogeneous)
+		pr_warning_once("Old SPE metadata, re-record to improve decode accuracy\n");
+		cpuid = perf_env__cpuid(spe->session->evlist->env);
+		midr = strtol(cpuid, NULL, 16);
+	} else {
+		/* CPU ID is -1 for per-thread mode */
+		if (speq->cpu < 0) {
+			/*
+			 * On the heterogeneous system, due to CPU ID is -1,
+			 * cannot confirm the data source packet is supported.
+			 */
+			if (!spe->is_homogeneous)
+				return false;
+
+			/* In homogeneous system, simply use CPU0's metadata */
+			if (spe->metadata)
+				metadata = spe->metadata[0];
+		} else {
+			metadata = arm_spe__get_metadata_by_cpu(spe, speq->cpu);
+		}
+
+		if (!metadata)
 			return false;
 
-		/* In homogeneous system, simply use CPU0's metadata */
-		if (spe->metadata)
-			metadata = spe->metadata[0];
-	} else {
-		metadata = arm_spe__get_metadata_by_cpu(spe, speq->cpu);
+		midr = metadata[ARM_SPE_CPU_MIDR];
 	}
-
-	if (!metadata)
-		return false;
-
-	midr = metadata[ARM_SPE_CPU_MIDR];
 
 	is_in_cpu_list = is_midr_in_range_list(midr, common_ds_encoding_cpus);
 	if (is_in_cpu_list)