[PATCH] fbdev: More accurate sync range extrapolation

The EDID block should specify the display's operating limits (vertical and
horizontal sync ranges, and maximum dot clock).  If not given by the EDID
block, the ranges are extrapolated from the modelist.  However, the
computation used is only a rough approximation, and the resulting values may
not reflect the actual capability of the display.  This problem is frequently
encountered when the EDID block has a single entry, the single mode entry will
fail validation.

To prevent this, calculate the values based on the same method used in
fb_validate_mode().

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/video/fbmon.c

@@ -605,6 +605,7 @@ static int fb_get_monitor_limits(unsigned char *edid, struct fb_monspecs *specs)
 	block = edid + DETAILED_TIMING_DESCRIPTIONS_START;
 
 	DPRINTK("      Monitor Operating Limits: ");
+
 	for (i = 0; i < 4; i++, block += DETAILED_TIMING_DESCRIPTION_SIZE) {
 		if (edid_is_limits_block(block)) {
 			specs->hfmin = H_MIN_RATE * 1000;
@@ -618,11 +619,12 @@ static int fb_get_monitor_limits(unsigned char *edid, struct fb_monspecs *specs)
 			break;
 		}
 	}
-	
+
 	/* estimate monitor limits based on modes supported */
 	if (retval) {
-		struct fb_videomode *modes;
+		struct fb_videomode *modes, *mode;
 		int num_modes, i, hz, hscan, pixclock;
+		int vtotal, htotal;
 
 		modes = fb_create_modedb(edid, &num_modes);
 		if (!modes) {
@@ -632,20 +634,38 @@ static int fb_get_monitor_limits(unsigned char *edid, struct fb_monspecs *specs)
 
 		retval = 0;
 		for (i = 0; i < num_modes; i++) {
-			hz = modes[i].refresh;
+			mode = &modes[i];
 			pixclock = PICOS2KHZ(modes[i].pixclock) * 1000;
-			hscan = (modes[i].yres * 105 * hz + 5000)/100;
+			htotal = mode->xres + mode->right_margin + mode->hsync_len
+				+ mode->left_margin;
+			vtotal = mode->yres + mode->lower_margin + mode->vsync_len
+				+ mode->upper_margin;
+
+			if (mode->vmode & FB_VMODE_INTERLACED)
+				vtotal /= 2;
+
+			if (mode->vmode & FB_VMODE_DOUBLE)
+				vtotal *= 2;
+
+			hscan = (pixclock + htotal / 2) / htotal;
+			hscan = (hscan + 500) / 1000 * 1000;
+			hz = (hscan + vtotal / 2) / vtotal;
 
 			if (specs->dclkmax == 0 || specs->dclkmax < pixclock)
 				specs->dclkmax = pixclock;
+
 			if (specs->dclkmin == 0 || specs->dclkmin > pixclock)
 				specs->dclkmin = pixclock;
+
 			if (specs->hfmax == 0 || specs->hfmax < hscan)
 				specs->hfmax = hscan;
+
 			if (specs->hfmin == 0 || specs->hfmin > hscan)
 				specs->hfmin = hscan;
+
 			if (specs->vfmax == 0 || specs->vfmax < hz)
 				specs->vfmax = hz;
+
 			if (specs->vfmin == 0 || specs->vfmin > hz)
 				specs->vfmin = hz;
 		}