[PATCH V2 4/6] tools/perf: Add powerpc callback support for arch_perf_record__need_read

[Athira Rajeev <atrajeev@linux.ibm.com>]

Implement the arch_perf_record__need_read() architecture-specific hook
for powerpc in arch/powerpc/util/evsel.c.

The HTM kernel driver sets event->count to 1 while data is staged in
its internal buffers and to 0 once the stream is exhausted.  This hook
reads that count for every open htm evsel via perf_evsel__read() and
accumulates the values.  A non-zero total means at least one HTM target
still has data pending; the recording loop added in the previous patch
will perform another mmap-read pass.

The implementation scans the evlist for htm events, iterates the fd/
sample-id xyarray, and skips any evsel whose fd and sample-id arrays are
mismatched to avoid reading stale state.  When the accumulated count
reaches zero the hook returns 0 and the recording loop proceeds to
disable and close the events.

Signed-off-by: Athira Rajeev <atrajeev@linux.ibm.com>
---
Changes in V2:
- Implements the renamed arch_perf_record__need_read() hook (V1
  implemented arch_record__collect_final_data()).
- Skips evsels whose fd and sample-id xyarrays are mismatched, avoiding
  stale-state reads.  V1 had no such guard.
- evlist__enable cycling is removed; that responsibility now belongs to
  the drain loop in builtin-record.c added in patch 3.
- File location changed to arch/powerpc/util/evsel.c (V1 used
  arch/powerpc/util/powerpc-htm.c).
- Patch is now 4/6 instead of 4/9.

 tools/perf/arch/powerpc/util/evsel.c | 69 ++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/tools/perf/arch/powerpc/util/evsel.c b/tools/perf/arch/powerpc/util/evsel.c
index 2f733cdc8dbb..8f2805a68026 100644
--- a/tools/perf/arch/powerpc/util/evsel.c
+++ b/tools/perf/arch/powerpc/util/evsel.c
@@ -1,8 +1,77 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
+#include <linux/string.h>
 #include "util/evsel.h"
+#include "util/record.h"
+#include "util/evlist.h"
+#include "util/debug.h"
+#include <internal/xyarray.h>
 
 void arch_evsel__set_sample_weight(struct evsel *evsel)
 {
 	evsel__set_sample_bit(evsel, WEIGHT_STRUCT);
 }
+
+/*
+ * Check if HTM events have more data to collect.
+ *
+ * This function reads the HTM event counts. When the kernel driver
+ * has more data available, it returns a non-zero count. When all
+ * data has been collected, it returns zero.
+ *
+ * Returns: 1 if more data exists, 0 if collection is complete
+ */
+int arch_perf_record__need_read(struct evlist *evlist)
+{
+	struct evsel *evsel;
+	bool found_htm = false;
+	u64 total_pending_bytes = 0;
+	int x, y;
+
+	/* there was an error during record__open */
+	if (!evlist)
+		return 0;
+
+	/* First, check if any HTM events exist */
+	evlist__for_each_entry(evlist, evsel) {
+		if (evsel->name && strstarts(evsel->name, "htm")) {
+			found_htm = true;
+			break;
+		}
+	}
+
+	if (!found_htm)
+		return 0;
+
+	/* Read HTM event counts to check if more data is available */
+	evlist__for_each_entry(evlist, evsel) {
+		struct xyarray *xy = evsel->core.sample_id;
+
+		if (!evsel->name || !strstarts(evsel->name, "htm"))
+			continue;
+
+		if (!strcmp(evsel->name, "dummy:u"))
+			continue;
+
+		if (xy == NULL || evsel->core.fd == NULL)
+			continue;
+
+		if (xyarray__max_x(evsel->core.fd) != xyarray__max_x(xy) ||
+		    xyarray__max_y(evsel->core.fd) != xyarray__max_y(xy)) {
+			pr_debug("Unmatched FD vs sample ID array for HTM event\n");
+			continue;
+		}
+
+		for (x = 0; x < xyarray__max_x(xy); x++) {
+			for (y = 0; y < xyarray__max_y(xy); y++) {
+				struct perf_counts_values count = { .val = 0 };
+
+				if (perf_evsel__read(&evsel->core, x, y, &count) == 0)
+					total_pending_bytes += count.val;
+			}
+		}
+	}
+
+	/* Collection is complete only when ALL hardware queues match 0 */
+	return (total_pending_bytes > 0) ? 1 : 0;
+}
-- 
2.43.0