[PATCH V3 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 the number of records still
staged in its internal buffers (total_size / record_size), 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 into
total_pending_records.  A non-zero total means at least one HTM target
still has records pending; the recording loop added in the previous
patch will perform another mmap-read pass.

The drain uses a two-layer safety check: event->count detects records
staged by the driver, and record__bytes_written() in the drain loop
confirms data was actually moved into perf.data.  This combination
handles the case where the driver count is briefly stale while hardware
is still flushing.

The implementation scans the evlist using evsel__pmu_name() to identify
HTM events by their kernel-assigned PMU name rather than the
user-visible event name, preventing false matches.  It 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 record
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 V3:
- Use evsel__pmu_name(evsel) instead of strstarts(evsel->name, "htm")
to identify HTM events, matching by kernel-assigned PMU name rather
than user-visible event name.
- Remove the redundant two-pass loop (first pass to set found_htm,
second to accumulate counts); a single pass with evsel__pmu_name()
is sufficient. if no HTM event exists total_pending_records stays 0
and the function returns 0.
- Remove the dead !strcmp(evsel->name, "dummy:u") check;
- evsel__pmu_name() will never return "htm" for a dummy:u software
event.
- Rename total_pending_bytes -> total_pending_records to match what
the driver actually reports (event->count = total_size / record_size,
a record count, not a byte count).
- Add #include <string.h> for musl compatibility (strcmp() without
it warns on some toolchains).

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 | 55 ++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/tools/perf/arch/powerpc/util/evsel.c b/tools/perf/arch/powerpc/util/evsel.c
index 2f733cdc8dbb..3c7ccc955b0a 100644
--- a/tools/perf/arch/powerpc/util/evsel.c
+++ b/tools/perf/arch/powerpc/util/evsel.c
@@ -1,8 +1,63 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
+#include <string.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;
+	u64 total_pending_records = 0;
+	int x, y;
+
+	/* there was an error during record__open */
+	if (!evlist)
+		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 (strcmp(evsel__pmu_name(evsel), "htm"))
+			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_records += count.val;
+			}
+		}
+	}
+
+	/* Collection is complete only when ALL hardware queues have no pending records */
+	return (total_pending_records > 0) ? 1 : 0;
+}
-- 
2.43.0