fbcon: add fbcon=margin:<color> command line option

This adds a new command line option to select the fbcon margin color.

The motivation for this is screens where black does not blend into the
physical surroundings of the screen. For example, using an LCD (not the
backlit kind), white text on a black background is hard to read, so
inverting the colors is preferred. However, when you do this, most of the
screen is filled with white but the margins are still filled with black.
This makes a big, black, backwards 'L' on the screen. By setting
fbcon=margin:7, the margins will be filled with white and the LCD looks as
expected.

Signed-off-by: David Lechner <[e-mail]>
[b.zolnierkie: ported over fbcon changes]
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

Documentation/fb/fbcon.txt

···
 	Actually, the underlying fb driver is totally ignorant of console
 	rotation.
 
+5. fbcon=margin:<color>
+
+	This option specifies the color of the margins. The margins are the
+	leftover area at the right and the bottom of the screen that are not
+	used by text. By default, this area will be black. The 'color' value
+	is 0 to 7 where 0 is black and 7 is white.
+
 C. Attaching, Detaching and Unloading
 
 Before going on how to attach, detach and unload the framebuffer console, an

drivers/video/fbdev/core/bitblit.c

···
 }
 
 static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
-			      int bottom_only)
+			      int color, int bottom_only)
 {
 	unsigned int cw = vc->vc_font.width;
 	unsigned int ch = vc->vc_font.height;
···
 	unsigned int bs = info->var.yres - bh;
 	struct fb_fillrect region;
 
-	region.color = 0;
+	region.color = color;
 	region.rop = ROP_COPY;
 
 	if (rw && !bottom_only) {

drivers/video/fbdev/core/fbcon.c

···
 /* console rotation */
 static int initial_rotation = -1;
 static int fbcon_has_sysfs;
+static int margin_color;
 
 static const struct consw fb_con;
 
···
 				initial_rotation = simple_strtoul(options, &options, 0);
 			if (initial_rotation > 3)
 				initial_rotation = 0;
+			continue;
+		}
+
+		if (!strncmp(options, "margin:", 7)) {
+			options += 7;
+			if (*options)
+				margin_color = simple_strtoul(options, &options, 0);
+			if (margin_color > 7)
+				margin_color = 0;
 			continue;
 		}
 	}
···
 	struct fbcon_ops *ops = info->fbcon_par;
 
 	if (!fbcon_is_inactive(vc, info))
-		ops->clear_margins(vc, info, bottom_only);
+		ops->clear_margins(vc, info, margin_color, bottom_only);
 }
 
 static void fbcon_cursor(struct vc_data *vc, int mode)

drivers/video/fbdev/core/fbcon.h

···
 		      const unsigned short *s, int count, int yy, int xx,
 		      int fg, int bg);
 	void (*clear_margins)(struct vc_data *vc, struct fb_info *info,
-			      int bottom_only);
+			      int color, int bottom_only);
 	void (*cursor)(struct vc_data *vc, struct fb_info *info, int mode,
 		       int softback_lines, int fg, int bg);
 	int  (*update_start)(struct fb_info *info);

drivers/video/fbdev/core/fbcon_ccw.c

···
 }
 
 static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
-			     int bottom_only)
+			      int color, int bottom_only)
 {
 	unsigned int cw = vc->vc_font.width;
 	unsigned int ch = vc->vc_font.height;
···
 	unsigned int bs = vc->vc_rows*ch;
 	struct fb_fillrect region;
 
-	region.color = 0;
+	region.color = color;
 	region.rop = ROP_COPY;
 
 	if (rw && !bottom_only) {

drivers/video/fbdev/core/fbcon_cw.c

···
 }
 
 static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
-			     int bottom_only)
+			     int color, int bottom_only)
 {
 	unsigned int cw = vc->vc_font.width;
 	unsigned int ch = vc->vc_font.height;
···
 	unsigned int rs = info->var.yres - rw;
 	struct fb_fillrect region;
 
-	region.color = 0;
+	region.color = color;
 	region.rop = ROP_COPY;
 
 	if (rw && !bottom_only) {

drivers/video/fbdev/core/fbcon_ud.c

···
 }
 
 static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
-			     int bottom_only)
+			     int color, int bottom_only)
 {
 	unsigned int cw = vc->vc_font.width;
 	unsigned int ch = vc->vc_font.height;
···
 	unsigned int bh = info->var.yres - (vc->vc_rows*ch);
 	struct fb_fillrect region;
 
-	region.color = 0;
+	region.color = color;
 	region.rop = ROP_COPY;
 
 	if (rw && !bottom_only) {

drivers/video/fbdev/core/tileblit.c

···
 }
 
 static void tile_clear_margins(struct vc_data *vc, struct fb_info *info,
-			       int bottom_only)
+			       int color, int bottom_only)
 {
 	return;
 }