drm/print: add drm_dbg_printer() for drm device specific printer

We've lacked a device specific debug printer. Add one. Take category
into account too.

__builtin_return_address(0) is inaccurate here, so don't use it. If
necessary, we can later pass __func__ to drm_dbg_printer() by wrapping
it inside a macro.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/48607d58e5cdf8341ffdd522257542fa2ce41a19.1705410327.git.jani.nikula@intel.com

drivers/gpu/drm/drm_print.c

@@ -189,6 +189,27 @@ void __drm_printfn_debug(struct drm_printer *p, struct va_format *vaf)
 }
 EXPORT_SYMBOL(__drm_printfn_debug);
 
+void __drm_printfn_dbg(struct drm_printer *p, struct va_format *vaf)
+{
+	const struct drm_device *drm = p->arg;
+	const struct device *dev = drm ? drm->dev : NULL;
+	enum drm_debug_category category = p->category;
+	const char *prefix = p->prefix ?: "";
+	const char *prefix_pad = p->prefix ? " " : "";
+
+	if (!__drm_debug_enabled(category))
+		return;
+
+	/* Note: __builtin_return_address(0) is useless here. */
+	if (dev)
+		dev_printk(KERN_DEBUG, dev, "[" DRM_NAME "]%s%s %pV",
+			   prefix_pad, prefix, vaf);
+	else
+		printk(KERN_DEBUG "[" DRM_NAME "]%s%s %pV",
+		       prefix_pad, prefix, vaf);
+}
+EXPORT_SYMBOL(__drm_printfn_dbg);
+
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf)
 {
 	struct drm_device *drm = p->arg;

include/drm/drm_print.h

@@ -176,6 +176,7 @@ struct drm_printer {
 	void (*puts)(struct drm_printer *p, const char *str);
 	void *arg;
 	const char *prefix;
+	enum drm_debug_category category;
 };
 
 void __drm_printfn_coredump(struct drm_printer *p, struct va_format *vaf);
@@ -184,6 +185,7 @@ void __drm_printfn_seq_file(struct drm_printer *p, struct va_format *vaf);
 void __drm_puts_seq_file(struct drm_printer *p, const char *str);
 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_printfn_dbg(struct drm_printer *p, struct va_format *vaf);
 void __drm_printfn_err(struct drm_printer *p, struct va_format *vaf);
 
 __printf(2, 3)
@@ -331,6 +333,28 @@ static inline struct drm_printer drm_debug_printer(const char *prefix)
 	return p;
 }
 
+/**
+ * drm_dbg_printer - construct a &drm_printer for drm device specific output
+ * @drm: the &struct drm_device pointer, or NULL
+ * @category: the debug category to use
+ * @prefix: debug output prefix, or NULL for no prefix
+ *
+ * RETURNS:
+ * The &drm_printer object
+ */
+static inline struct drm_printer drm_dbg_printer(struct drm_device *drm,
+						 enum drm_debug_category category,
+						 const char *prefix)
+{
+	struct drm_printer p = {
+		.printfn = __drm_printfn_dbg,
+		.arg = drm,
+		.prefix = prefix,
+		.category = category,
+	};
+	return p;
+}
+
 /**
  * drm_err_printer - construct a &drm_printer that outputs to drm_err()
  * @drm: the &struct drm_device pointer