tridentfb: improve check_var function

Do some additional checks (like pixelclock versus ramdac speed) to
eliminate modes which do not work.
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/tridentfb.c

@@ -829,6 +829,7 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
 {
 	struct tridentfb_par *par = info->par;
 	int bpp = var->bits_per_pixel;
+	int ramdac = 230000; /* 230MHz for most 3D chips */
 	debug("enter\n");
 
 	/* check color depth */
@@ -837,6 +838,12 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
 	/* check whether resolution fits on panel and in memory */
 	if (par->flatpanel && nativex && var->xres > nativex)
 		return -EINVAL;
+	/* various resolution checks */
+	var->xres = (var->xres + 7) & ~0x7;
+	if (var->xres != var->xres_virtual)
+		var->xres_virtual = var->xres;
+	if (var->yres > var->yres_virtual)
+		var->yres_virtual = var->yres;
 	if (var->xres * var->yres_virtual * bpp / 8 > info->fix.smem_len)
 		return -EINVAL;
 
@@ -868,6 +875,33 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
 	default:
 		return -EINVAL;
 	}
+
+	if (is_xp(par->chip_id))
+		ramdac = 350000;
+
+	switch (par->chip_id) {
+	case TGUI9440:
+		ramdac = 90000;
+		break;
+	case CYBER9320:
+	case TGUI9660:
+		ramdac = 135000;
+		break;
+	case PROVIDIA9685:
+	case CYBER9388:
+	case CYBER9382:
+	case CYBER9385:
+		ramdac = 170000;
+		break;
+	}
+
+	/* The clock is doubled for 32 bpp */
+	if (bpp == 32)
+		ramdac /= 2;
+
+	if (PICOS2KHZ(var->pixclock) > ramdac)
+		return -EINVAL;
+
 	debug("exit\n");
 
 	return 0;