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>

2 files changed, 151 insertions, 0 deletions

diff --git a/arch/s390/include/asm/debug.h b/arch/s390/include/asm/debug.h
index 9b8fdaa97219..19a55e1e3a0c 100644
--- a/arch/s390/include/asm/debug.h
+++ b/arch/s390/include/asm/debug.h
@@ -13,6 +13,7 @@
 #include <linux/time.h>
 #include <linux/refcount.h>
 #include <linux/fs.h>
+#include <linux/init.h>
 
 #define DEBUG_MAX_LEVEL		   6  /* debug levels range from 0 to 6 */
 #define DEBUG_OFF_LEVEL		   -1 /* level where debug is switched off */
@@ -391,4 +392,99 @@ int debug_register_view(debug_info_t *id, struct debug_view *view);
 
 int debug_unregister_view(debug_info_t *id, struct debug_view *view);
 
+#ifndef MODULE
+
+/*
+ * Note: Initial page and area numbers must be fixed to allow static
+ * initialization. This enables very early tracing. Changes to these values
+ * must be reflected in __DEFINE_STATIC_AREA.
+ */
+#define EARLY_PAGES		8
+#define EARLY_AREAS		1
+
+#define VNAME(var, suffix)	__##var##_##suffix
+
+/*
+ * Define static areas for early trace data. During boot debug_register_static()
+ * will replace these with dynamically allocated areas to allow custom page and
+ * area sizes, and dynamic resizing.
+ */
+#define __DEFINE_STATIC_AREA(var)					\
+static char VNAME(var, data)[EARLY_PAGES][PAGE_SIZE] __initdata;	\
+static debug_entry_t *VNAME(var, pages)[EARLY_PAGES] __initdata = {	\
+	(debug_entry_t *)VNAME(var, data)[0],				\
+	(debug_entry_t *)VNAME(var, data)[1],				\
+	(debug_entry_t *)VNAME(var, data)[2],				\
+	(debug_entry_t *)VNAME(var, data)[3],				\
+	(debug_entry_t *)VNAME(var, data)[4],				\
+	(debug_entry_t *)VNAME(var, data)[5],				\
+	(debug_entry_t *)VNAME(var, data)[6],				\
+	(debug_entry_t *)VNAME(var, data)[7],				\
+};									\
+static debug_entry_t **VNAME(var, areas)[EARLY_AREAS] __initdata = {	\
+	(debug_entry_t **)VNAME(var, pages),				\
+};									\
+static int VNAME(var, active_pages)[EARLY_AREAS] __initdata;		\
+static int VNAME(var, active_entries)[EARLY_AREAS] __initdata
+
+#define __DEBUG_INFO_INIT(var, _name, _buf_size) {			\
+	.next = NULL,							\
+	.prev = NULL,							\
+	.ref_count = REFCOUNT_INIT(1),					\
+	.lock = __SPIN_LOCK_UNLOCKED(var.lock),				\
+	.level = DEBUG_DEFAULT_LEVEL,					\
+	.nr_areas = EARLY_AREAS,					\
+	.pages_per_area = EARLY_PAGES,					\
+	.buf_size = (_buf_size),					\
+	.entry_size = sizeof(debug_entry_t) + (_buf_size),		\
+	.areas = VNAME(var, areas),					\
+	.active_area = 0,						\
+	.active_pages = VNAME(var, active_pages),			\
+	.active_entries = VNAME(var, active_entries),			\
+	.debugfs_root_entry = NULL,					\
+	.debugfs_entries = { NULL },					\
+	.views = { NULL },						\
+	.name = (_name),						\
+	.mode = 0600,							\
+}
+
+#define __REGISTER_STATIC_DEBUG_INFO(var, name, pages, areas, view)	\
+static int __init VNAME(var, reg)(void)					\
+{									\
+	debug_register_static(&var, (pages), (areas));			\
+	debug_register_view(&var, (view));				\
+	return 0;							\
+}									\
+arch_initcall(VNAME(var, reg))
+
+/**
+ * DEFINE_STATIC_DEBUG_INFO - Define static debug_info_t
+ *
+ * @var: Name of debug_info_t variable
+ * @name: Name of debug log (e.g. used for debugfs entry)
+ * @pages_per_area: Number of pages per area
+ * @nr_areas: Number of debug areas
+ * @buf_size: Size of data area in each debug entry
+ * @view: Pointer to debug view struct
+ *
+ * Define a static debug_info_t for early tracing. The associated debugfs log
+ * is automatically registered with the specified debug view.
+ *
+ * Important: Users of this macro must not call any of the
+ * debug_register/_unregister() functions for this debug_info_t!
+ *
+ * Note: Tracing will start with a fixed number of initial pages and areas.
+ * The debug area will be changed to use the specified numbers during
+ * arch_initcall.
+ */
+#define DEFINE_STATIC_DEBUG_INFO(var, name, pages, nr_areas, buf_size, view) \
+__DEFINE_STATIC_AREA(var);						\
+static debug_info_t __refdata var =					\
+	__DEBUG_INFO_INIT(var, (name), (buf_size));			\
+__REGISTER_STATIC_DEBUG_INFO(var, name, pages, nr_areas, view)
+
+void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas);
+
+#endif /* MODULE */
+
 #endif /* DEBUG_H */
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)
 {