drm/printer: add debug printer

Useful for dumping lots of data into dmesg, e.g. drm_mm.

v2: Fixup export_symbol line, I misplaced a hunk (Chris).

Cc: Rob Clark <robdclark@gmail.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1482943330-11592-1-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_print.c

@@ -40,6 +40,12 @@ void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_info);
 
+void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf)
+{
+	pr_debug("%s %pV", p->prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_debug);
+
 /**
  * drm_printf - print to a &drm_printer stream
  * @p: the &drm_printer

include/drm/drm_print.h

@@ -60,19 +60,20 @@
 
 /**
  * struct drm_printer - drm output "stream"
- * @printfn: actual output fxn
- * @arg: output fxn specific data
  *
  * Do not use struct members directly.  Use drm_printer_seq_file(),
  * drm_printer_info(), etc to initialize.  And drm_printf() for output.
  */
 struct drm_printer {
+	/* private: */
 	void (*printfn)(struct drm_printer *p, struct va_format *vaf);
 	void *arg;
+	const char *prefix;
 };
 
 void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_info(struct drm_printer *p, struct va_format *vaf);
+void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf);
 
 void drm_printf(struct drm_printer *p, const char *f, ...);
 
@@ -109,4 +110,19 @@ static inline struct drm_printer drm_info_printer(struct device *dev)
 	return p;
 }
 
+/**
+ * drm_debug_printer - construct a &drm_printer that outputs to pr_debug()
+ * @prefix: debug output prefix
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_debug_printer(const char *prefix)
+{
+	struct drm_printer p = {
+		.printfn = __drm_printfn_debug,
+		.prefix = prefix
+	};
+	return p;
+}
 #endif /* DRM_PRINT_H_ */