ARM: 9480/1: entry: expand comment in __switch_tografted

As per discussion between the developers in the mail thread
linked, expand the comment in __switch_to so that readers
of the code understand what is going on.

Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 71 insertions, 0 deletions

diff --git a/tools/perf/util/rwsem.c b/tools/perf/util/rwsem.c
new file mode 100644
index 000000000..9d2683239
--- /dev/null
+++ b/tools/perf/util/rwsem.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "util.h"
+#include "rwsem.h"
+
+#if RWS_ERRORCHECK
+#include "mutex.h"
+#endif
+
+int init_rwsem(struct rw_semaphore *sem)
+{
+#if RWS_ERRORCHECK
+	mutex_init(&sem->mtx);
+	return 0;
+#else
+	return pthread_rwlock_init(&sem->lock, NULL);
+#endif
+}
+
+int exit_rwsem(struct rw_semaphore *sem)
+{
+#if RWS_ERRORCHECK
+	mutex_destroy(&sem->mtx);
+	return 0;
+#else
+	return pthread_rwlock_destroy(&sem->lock);
+#endif
+}
+
+int down_read(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_lock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_rdlock(&sem->lock);
+#endif
+}
+
+int up_read(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_unlock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_unlock(&sem->lock);
+#endif
+}
+
+int down_write(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_lock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_wrlock(&sem->lock);
+#endif
+}
+
+int up_write(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_unlock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_unlock(&sem->lock);
+#endif
+}