drm: Print pretty names for pixel formats

Rather than just printing the pixel format as a hex number, decode the
fourcc into human readable form, and also decode the LE vs. BE flag.

Keep printing the raw hex number too in case it contains non-printable
characters.

Some examples what the new drm_get_format_name() produces:
DRM_FORMAT_XRGB8888: "XR24 little-endian (0x34325258)"
DRM_FORMAT_YUYV: "YUYV little-endian (0x56595559)"
DRM_FORMAT_RGB565|DRM_FORMAT_BIG_ENDIAN: "RG16 big-endian (0xb6314752)"
Unprintable characters: "D??? big-endian (0xff7f0244)"

v2: Fix patch author
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc.c

@@ -29,6 +29,7 @@
  *      Dave Airlie <airlied@linux.ie>
  *      Jesse Barnes <jesse.barnes@intel.com>
  */
+#include <linux/ctype.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/export.h>
@@ -252,6 +253,28 @@ char *drm_get_connector_status_name(enum drm_connector_status status)
 }
 EXPORT_SYMBOL(drm_get_connector_status_name);
 
+static char printable_char(int c)
+{
+	return isascii(c) && isprint(c) ? c : '?';
+}
+
+char *drm_get_format_name(uint32_t format)
+{
+	static char buf[32];
+
+	snprintf(buf, sizeof(buf),
+		 "%c%c%c%c %s-endian (0x%08x)",
+		 printable_char(format & 0xff),
+		 printable_char((format >> 8) & 0xff),
+		 printable_char((format >> 16) & 0xff),
+		 printable_char((format >> 24) & 0x7f),
+		 format & DRM_FORMAT_BIG_ENDIAN ? "big" : "little",
+		 format);
+
+	return buf;
+}
+EXPORT_SYMBOL(drm_get_format_name);
+
 /**
  * drm_mode_object_get - allocate a new modeset identifier
  * @dev: DRM device
@@ -1834,7 +1857,8 @@ int drm_mode_setplane(struct drm_device *dev, void *data,
 		if (fb->pixel_format == plane->format_types[i])
 			break;
 	if (i == plane->format_count) {
-		DRM_DEBUG_KMS("Invalid pixel format 0x%08x\n", fb->pixel_format);
+		DRM_DEBUG_KMS("Invalid pixel format %s\n",
+			      drm_get_format_name(fb->pixel_format));
 		ret = -EINVAL;
 		goto out;
 	}
@@ -2312,7 +2336,8 @@ static int framebuffer_check(const struct drm_mode_fb_cmd2 *r)
 
 	ret = format_check(r);
 	if (ret) {
-		DRM_DEBUG_KMS("bad framebuffer format 0x%08x\n", r->pixel_format);
+		DRM_DEBUG_KMS("bad framebuffer format %s\n",
+			      drm_get_format_name(r->pixel_format));
 		return ret;
 	}
 

include/drm/drm_crtc.h

@@ -1094,5 +1094,6 @@ extern int drm_format_num_planes(uint32_t format);
 extern int drm_format_plane_cpp(uint32_t format, int plane);
 extern int drm_format_horz_chroma_subsampling(uint32_t format);
 extern int drm_format_vert_chroma_subsampling(uint32_t format);
+extern char *drm_get_format_name(uint32_t format);
 
 #endif /* __DRM_CRTC_H__ */