cirrusfb: check_par fixes

1. Check if virtual resolution fits into memory.
   Otherwise, Linux hangs during panning.
2. When selected use all available memory to
    maximize yres_virtual to speed up panning
   (previously also xres_virtual was increased).
3. Simplify memory restriction calculations.

Signed-off-by: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 41 deletions

diff --git a/drivers/video/cirrusfb.c b/drivers/video/cirrusfb.c
index c14b2435d23e..e729fb279645 100644
--- a/drivers/video/cirrusfb.c
+++ b/drivers/video/cirrusfb.c
@@ -628,27 +628,18 @@ static long cirrusfb_get_mclk(long freq, int bpp, long *div)
 static int cirrusfb_check_var(struct fb_var_screeninfo *var,
                               struct fb_info *info)
 {
-        int nom, den;           /* translyting from pixels->bytes */
-        int yres, i;
-        static struct { int xres, yres; } modes[] =
-        { { 1600, 1280 },
-          { 1280, 1024 },
-          { 1024, 768 },
-          { 800, 600 },
-          { 640, 480 },
-          { -1, -1 } };
+        int yres;
+        /* memory size in pixels */
+        unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
 
         switch (var->bits_per_pixel) {
         case 1:
-                nom = 4;
-                den = 8;
+                pixels /= 4;
                 break;          /* 8 pixel per byte, only 1/4th of mem usable */
         case 8:
         case 16:
         case 24:
         case 32:
-                nom = var->bits_per_pixel / 8;
-                den = 1;
                 break;          /* 1 pixel == 1 byte */
         default:
                 printk(KERN_ERR "cirrusfb: mode %dx%dx%d rejected..."
@@ -658,43 +649,29 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
                 return -EINVAL;
         }
 
-        if (var->xres * nom / den * var->yres > info->screen_size) {
-                printk(KERN_ERR "cirrusfb: mode %dx%dx%d rejected..."
-                        "resolution too high to fit into video memory!\n",
-                        var->xres, var->yres, var->bits_per_pixel);
-                DPRINTK("EXIT - EINVAL error\n");
-                return -EINVAL;
-        }
-
+        if (var->xres_virtual < var->xres)
+                var->xres_virtual = var->xres;
         /* use highest possible virtual resolution */
-        if (var->xres_virtual == -1 &&
-            var->yres_virtual == -1) {
-                printk(KERN_INFO
-                     "cirrusfb: using maximum available virtual resolution\n");
-                for (i = 0; modes[i].xres != -1; i++) {
-                        int size = modes[i].xres * nom / den * modes[i].yres;
-                        if (size < info->screen_size / 2)
-                                break;
-                }
-                if (modes[i].xres == -1) {
-                        printk(KERN_ERR "cirrusfb: could not find a virtual "
-                                "resolution that fits into video memory!!\n");
-                        DPRINTK("EXIT - EINVAL error\n");
-                        return -EINVAL;
-                }
-                var->xres_virtual = modes[i].xres;
-                var->yres_virtual = modes[i].yres;
+        if (var->yres_virtual == -1) {
+                var->yres_virtual = pixels / var->xres_virtual;
 
                 printk(KERN_INFO "cirrusfb: virtual resolution set to "
                         "maximum of %dx%d\n", var->xres_virtual,
                         var->yres_virtual);
         }
-
-        if (var->xres_virtual < var->xres)
-                var->xres_virtual = var->xres;
         if (var->yres_virtual < var->yres)
                 var->yres_virtual = var->yres;
 
+        if (var->xres_virtual * var->yres_virtual > pixels) {
+                printk(KERN_ERR "cirrusfb: mode %dx%dx%d rejected... "
+                      "virtual resolution too high to fit into video memory!\n",
+                        var->xres_virtual, var->yres_virtual,
+                        var->bits_per_pixel);
+                DPRINTK("EXIT - EINVAL error\n");
+                return -EINVAL;
+        }
+
+
         if (var->xoffset < 0)
                 var->xoffset = 0;
         if (var->yoffset < 0)