s390/debug: add early tracing support

Debug areas can currently only be used after s390dbf initialization
which occurs as a postcore_initcall. This is too late for tracing
earlier code such as that related to console_init().

This patch introduces a macro for defining a statically initialized
debug area that can be used to trace very early code. The macro is made
available for built-in code only because modules are never running
during early boot.

Example usage:

1. Define static debug area:

  DEFINE_STATIC_DEBUG_INFO(my_debug, "my_debug", 4, 1, 16,
			   &debug_hex_ascii_view);

2. Add trace entry:

  debug_event(&my_debug, 0, "DATA", 4);

Note: The debug area is automatically registered in debugfs during boot.
      A driver must not call any of the debug_register()/_unregister()
      functions on a static debug_info_t!

Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index 05b765b8038e..da4d67736daa 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -692,6 +692,61 @@ debug_info_t *debug_register(const char *name, int pages_per_area,
 }
 EXPORT_SYMBOL(debug_register);
 
+/**
+ * debug_register_static() - registers a static debug area
+ *
+ * @id: Handle for static debug area
+ * @pages_per_area: Number of pages per area
+ * @nr_areas: Number of debug areas
+ *
+ * Register debug_info_t defined using DEFINE_STATIC_DEBUG_INFO.
+ *
+ * Note: This function is called automatically via an initcall generated by
+ *	 DEFINE_STATIC_DEBUG_INFO.
+ */
+void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas)
+{
+	unsigned long flags;
+	debug_info_t *copy;
+
+	if (!initialized) {
+		pr_err("Tried to register debug feature %s too early\n",
+		       id->name);
+		return;
+	}
+
+	copy = debug_info_alloc("", pages_per_area, nr_areas, id->buf_size,
+				id->level, ALL_AREAS);
+	if (!copy) {
+		pr_err("Registering debug feature %s failed\n", id->name);
+
+		/* Clear pointers to prevent tracing into released initdata. */
+		spin_lock_irqsave(&id->lock, flags);
+		id->areas = NULL;
+		id->active_pages = NULL;
+		id->active_entries = NULL;
+		spin_unlock_irqrestore(&id->lock, flags);
+
+		return;
+	}
+
+	/* Replace static trace area with dynamic copy. */
+	spin_lock_irqsave(&id->lock, flags);
+	debug_events_append(copy, id);
+	debug_areas_swap(id, copy);
+	spin_unlock_irqrestore(&id->lock, flags);
+
+	/* Clear pointers to initdata and discard copy. */
+	copy->areas = NULL;
+	copy->active_pages = NULL;
+	copy->active_entries = NULL;
+	debug_info_free(copy);
+
+	mutex_lock(&debug_mutex);
+	_debug_register(id);
+	mutex_unlock(&debug_mutex);
+}
+
 /* Remove debugfs entries and remove from internal list. */
 static void _debug_unregister(debug_info_t *id)
 {