drm: Add DRM_DEBUG_VBL()

Add a new debug class for _verbose_ debug message from the vblank code.
That is message we spew out potentially for every vblank interrupt.
Thierry already got annoyed at the spew, and now I managed to lock up
my box with these debug prints (seems serial console + a few debug
prints every vblank aren't a good combination).

Or should I maybe call it DRM_DEBUG_IRQ?

Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drmP.h

@@ -107,6 +107,9 @@ struct dma_buf_attachment;
  * ATOMIC: used in the atomic code.
  *	  This is the category used by the DRM_DEBUG_ATOMIC() macro.
  *
+ * VBL: used for verbose debug message in the vblank code
+ *	  This is the category used by the DRM_DEBUG_VBL() macro.
+ *
  * Enabling verbose debug messages is done through the drm.debug parameter,
  * each category being enabled by a bit.
  *
@@ -114,7 +117,7 @@ struct dma_buf_attachment;
  * drm.debug=0x2 will enable DRIVER messages
  * drm.debug=0x3 will enable CORE and DRIVER messages
  * ...
- * drm.debug=0xf will enable all messages
+ * drm.debug=0x3f will enable all messages
  *
  * An interesting feature is that it's possible to enable verbose logging at
  * run-time by echoing the debug value in its sysfs node:
@@ -125,6 +128,7 @@ struct dma_buf_attachment;
 #define DRM_UT_KMS		0x04
 #define DRM_UT_PRIME		0x08
 #define DRM_UT_ATOMIC		0x10
+#define DRM_UT_VBL		0x20
 
 extern __printf(2, 3)
 void drm_ut_debug_printk(const char *function_name,
@@ -217,6 +221,11 @@ void drm_err(const char *format, ...);
 		if (unlikely(drm_debug & DRM_UT_ATOMIC))		\
 			drm_ut_debug_printk(__func__, fmt, ##args);	\
 	} while (0)
+#define DRM_DEBUG_VBL(fmt, args...)					\
+	do {								\
+		if (unlikely(drm_debug & DRM_UT_VBL))			\
+			drm_ut_debug_printk(__func__, fmt, ##args);	\
+	} while (0)
 
 /*@}*/