perf test: Implement skip_reason callback for watchpoint tests

Currently reason for skipping the read only watchpoint test is only seen
when running in verbose mode:

  $ perf test watchpoint
  23: Watchpoint                                            :
  23.1: Read Only Watchpoint                                : Skip
  23.2: Write Only Watchpoint                               : Ok
  23.3: Read / Write Watchpoint                             : Ok
  23.4: Modify Watchpoint                                   : Ok

  $ perf test -v watchpoint
  23: Watchpoint                                            :
  23.1: Read Only Watchpoint                                :
  --- start ---
  test child forked, pid 60204
  Hardware does not support read only watchpoints.
  test child finished with -2

Implement skip_reason callback for the watchpoint tests, so that it's
easy to see reason why the test is skipped:

  $ perf test watchpoint
  23: Watchpoint                                            :
  23.1: Read Only Watchpoint                                : Skip (missing hardware support)
  23.2: Write Only Watchpoint                               : Ok
  23.3: Read / Write Watchpoint                             : Ok
  23.4: Modify Watchpoint                                   : Ok

Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20201016131650.72476-1-tommi.t.rantala@nokia.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/builtin-test.c

@@ -142,6 +142,7 @@ static struct test generic_tests[] = {
 			.skip_if_fail	= false,
 			.get_nr		= test__wp_subtest_get_nr,
 			.get_desc	= test__wp_subtest_get_desc,
+			.skip_reason    = test__wp_subtest_skip_reason,
 		},
 	},
 	{

tools/perf/tests/tests.h

@@ -66,6 +66,7 @@ int test__bp_signal_overflow(struct test *test, int subtest);
 int test__bp_accounting(struct test *test, int subtest);
 int test__wp(struct test *test, int subtest);
 const char *test__wp_subtest_get_desc(int subtest);
+const char *test__wp_subtest_skip_reason(int subtest);
 int test__wp_subtest_get_nr(void);
 int test__task_exit(struct test *test, int subtest);
 int test__mem(struct test *test, int subtest);

tools/perf/tests/wp.c

@@ -174,10 +174,12 @@ static bool wp_ro_supported(void)
 #endif
 }
 
-static void wp_ro_skip_msg(void)
+static const char *wp_ro_skip_msg(void)
 {
 #if defined (__x86_64__) || defined (__i386__)
-	pr_debug("Hardware does not support read only watchpoints.\n");
+	return "missing hardware support";
+#else
+	return NULL;
 #endif
 }
 
@@ -185,7 +187,7 @@ static struct {
 	const char *desc;
 	int (*target_func)(void);
 	bool (*is_supported)(void);
-	void (*skip_msg)(void);
+	const char *(*skip_msg)(void);
 } wp_testcase_table[] = {
 	{
 		.desc = "Read Only Watchpoint",
@@ -219,16 +221,23 @@ const char *test__wp_subtest_get_desc(int i)
 	return wp_testcase_table[i].desc;
 }
 
+const char *test__wp_subtest_skip_reason(int i)
+{
+	if (i < 0 || i >= (int)ARRAY_SIZE(wp_testcase_table))
+		return NULL;
+	if (!wp_testcase_table[i].skip_msg)
+		return NULL;
+	return wp_testcase_table[i].skip_msg();
+}
+
 int test__wp(struct test *test __maybe_unused, int i)
 {
 	if (i < 0 || i >= (int)ARRAY_SIZE(wp_testcase_table))
 		return TEST_FAIL;
 
 	if (wp_testcase_table[i].is_supported &&
-	    !wp_testcase_table[i].is_supported()) {
-		wp_testcase_table[i].skip_msg();
+	    !wp_testcase_table[i].is_supported())
 		return TEST_SKIP;
-	}
 
 	return !wp_testcase_table[i].target_func() ? TEST_OK : TEST_FAIL;
 }