sm501fb: fix timing limits

Vertical sync height register can only hold 6 bits.  Fix the hsync start test
to use > instead of >=.  Also add a few clarifying comments.
Signed-off-by: Ville Syrjala <syrjala@sci.fi>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/sm501fb.c

@@ -237,12 +237,14 @@ static int sm501fb_check_var(struct fb_var_screeninfo *var,
 
 	/* check we can fit these values into the registers */
 
-	if (var->hsync_len > 255 || var->vsync_len > 255)
+	if (var->hsync_len > 255 || var->vsync_len > 63)
 		return -EINVAL;
 
-	if ((var->xres + var->right_margin) >= 4096)
+	/* hdisplay end and hsync start */
+	if ((var->xres + var->right_margin) > 4096)
 		return -EINVAL;
 
+	/* vdisplay end and vsync start */
 	if ((var->yres + var->lower_margin) > 2048)
 		return -EINVAL;