tridentfb: y-panning fixes

The Trident cards uses only 20-bit address of screen start in double
words.  This allows addressing for only 4MB of video memory so check this.

Also remove some redundant checks and assignments.

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

1 files changed, 4 insertions, 5 deletions

diff --git a/drivers/video/tridentfb.c b/drivers/video/tridentfb.c
index 1c3f0ba4b33a..138140bdb495 100644
--- a/drivers/video/tridentfb.c
+++ b/drivers/video/tridentfb.c
@@ -870,8 +870,10 @@ static int tridentfb_check_var(struct fb_var_screeninfo *var,
                 line_length = var->xres_virtual * bpp / 8;
         }
 
-        if (var->yres > var->yres_virtual)
-                var->yres_virtual = var->yres;
+        /* datasheet specifies how to set panning only up to 4 MB */
+        if (line_length * (var->yres_virtual - var->yres) > (4 << 20))
+                var->yres_virtual = ((4 << 20) / line_length) + var->yres;
+
         if (line_length * var->yres_virtual > info->fix.smem_len)
                 return -EINVAL;
 
@@ -944,8 +946,6 @@ static int tridentfb_pan_display(struct fb_var_screeninfo *var,
         debug("enter\n");
         offset = (var->xoffset + (var->yoffset * var->xres_virtual))
                 * var->bits_per_pixel / 32;
-        info->var.xoffset = var->xoffset;
-        info->var.yoffset = var->yoffset;
         set_screen_start(par, offset);
         debug("exit\n");
         return 0;
@@ -1225,7 +1225,6 @@ static int tridentfb_setcolreg(unsigned regno, unsigned red, unsigned green,
                                 ((blue & 0xFF00) >> 8);
         }
 
-/*      debug("exit\n"); */
         return 0;
 }