drm: add DRM_ERROR_RATELIMITED

For error traces in situations that can run away, it is nice to have a
rate-limited version of DRM_ERROR() to avoid massive log flooding.
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drmP.h

@@ -56,6 +56,7 @@
 #include <linux/mutex.h>
 #include <linux/io.h>
 #include <linux/slab.h>
+#include <linux/ratelimit.h>
 #if defined(__alpha__) || defined(__powerpc__)
 #include <asm/pgtable.h>	/* For pte_wrprotect */
 #endif
@@ -180,6 +181,22 @@ int drm_err(const char *func, const char *format, ...);
 #define DRM_ERROR(fmt, ...)				\
 	drm_err(__func__, fmt, ##__VA_ARGS__)
 
+/**
+ * Rate limited error output.  Like DRM_ERROR() but won't flood the log.
+ *
+ * \param fmt printf() like format string.
+ * \param arg arguments
+ */
+#define DRM_ERROR_RATELIMITED(fmt, ...)				\
+({									\
+	static DEFINE_RATELIMIT_STATE(_rs,				\
+				      DEFAULT_RATELIMIT_INTERVAL,	\
+				      DEFAULT_RATELIMIT_BURST);		\
+									\
+	if (__ratelimit(&_rs))						\
+		drm_err(__func__, fmt, ##__VA_ARGS__);			\
+})
+
 #define DRM_INFO(fmt, ...)				\
 	printk(KERN_INFO "[" DRM_NAME "] " fmt, ##__VA_ARGS__)