fbdev: Add FOURCC-based format configuration API

This API will be used to support YUV frame buffer formats in a standard
way.

Last but not least, create a much needed fbdev API documentation and
document the format setting APIs.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>

drivers/video/fbmem.c

@@ -967,6 +967,20 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 	    memcmp(&info->var, var, sizeof(struct fb_var_screeninfo))) {
 		u32 activate = var->activate;
 
+		/* When using FOURCC mode, make sure the red, green, blue and
+		 * transp fields are set to 0.
+		 */
+		if ((info->fix.capabilities & FB_CAP_FOURCC) &&
+		    var->grayscale > 1) {
+			if (var->red.offset     || var->green.offset    ||
+			    var->blue.offset    || var->transp.offset   ||
+			    var->red.length     || var->green.length    ||
+			    var->blue.length    || var->transp.length   ||
+			    var->red.msb_right  || var->green.msb_right ||
+			    var->blue.msb_right || var->transp.msb_right)
+				return -EINVAL;
+		}
+
 		if (!info->fbops->fb_check_var) {
 			*var = info->var;
 			goto done;

include/linux/fb.h

@@ -45,6 +45,7 @@
 #define FB_TYPE_INTERLEAVED_PLANES	2	/* Interleaved planes	*/
 #define FB_TYPE_TEXT			3	/* Text/attributes	*/
 #define FB_TYPE_VGA_PLANES		4	/* EGA/VGA planes	*/
+#define FB_TYPE_FOURCC			5	/* Type identified by a V4L2 FOURCC */
 
 #define FB_AUX_TEXT_MDA		0	/* Monochrome text */
 #define FB_AUX_TEXT_CGA		1	/* CGA/EGA/VGA Color text */
@@ -69,6 +70,7 @@
 #define FB_VISUAL_PSEUDOCOLOR		3	/* Pseudo color (like atari) */
 #define FB_VISUAL_DIRECTCOLOR		4	/* Direct color */
 #define FB_VISUAL_STATIC_PSEUDOCOLOR	5	/* Pseudo color readonly */
+#define FB_VISUAL_FOURCC		6	/* Visual identified by a V4L2 FOURCC */
 
 #define FB_ACCEL_NONE		0	/* no hardware accelerator	*/
 #define FB_ACCEL_ATARIBLITT	1	/* Atari Blitter		*/
@@ -154,6 +156,8 @@
 
 #define FB_ACCEL_PUV3_UNIGFX	0xa0	/* PKUnity-v3 Unigfx		*/
 
+#define FB_CAP_FOURCC		1	/* Device supports FOURCC-based formats */
+
 struct fb_fix_screeninfo {
 	char id[16];			/* identification string eg "TT Builtin" */
 	unsigned long smem_start;	/* Start of frame buffer mem */
@@ -171,7 +175,8 @@ struct fb_fix_screeninfo {
 	__u32 mmio_len;			/* Length of Memory Mapped I/O  */
 	__u32 accel;			/* Indicate to driver which	*/
 					/*  specific chip/card we have	*/
-	__u16 reserved[3];		/* Reserved for future compatibility */
+	__u16 capabilities;		/* see FB_CAP_*			*/
+	__u16 reserved[2];		/* Reserved for future compatibility */
 };
 
 /* Interpretation of offset for color fields: All offsets are from the right,
@@ -246,8 +251,8 @@ struct fb_var_screeninfo {
 	__u32 yoffset;			/* resolution			*/
 
 	__u32 bits_per_pixel;		/* guess what			*/
-	__u32 grayscale;		/* != 0 Graylevels instead of colors */
-
+	__u32 grayscale;		/* 0 = color, 1 = grayscale,	*/
+					/* >1 = FOURCC			*/
 	struct fb_bitfield red;		/* bitfield in fb mem if true color, */
 	struct fb_bitfield green;	/* else only length is significant */
 	struct fb_bitfield blue;
@@ -273,7 +278,8 @@ struct fb_var_screeninfo {
 	__u32 sync;			/* see FB_SYNC_*		*/
 	__u32 vmode;			/* see FB_VMODE_*		*/
 	__u32 rotate;			/* angle we rotate counter clockwise */
-	__u32 reserved[5];		/* Reserved for future compatibility */
+	__u32 colorspace;		/* colorspace for FOURCC-based modes */
+	__u32 reserved[4];		/* Reserved for future compatibility */
 };
 
 struct fb_cmap {