Re: [Linux-fbdev-devel] [PATCH] tridentfb: y-panning fixes

[Krzysztof H. <krz...@po...>]

From: Krzysztof Helt <krz...@wp...>

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 <krz...@wp...>

--- 
The previous patch have had wrong description. The start screen
address is 20-bit in double words (4-bytes) which is exactly 4MB.

diff -urp linux-old/drivers/video/tridentfb.c linux-new/drivers/video/tridentfb.c
--- linux-old/drivers/video/tridentfb.c	2008-05-29 00:11:27.177498740 +0200
+++ linux-new/drivers/video/tridentfb.c	2008-05-29 00:08:02.957495446 +0200
@@ -870,8 +870,10 @@ static int tridentfb_check_var(struct fb
 		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 
 	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 
 				((blue & 0xFF00) >> 8);
 	}
 
-/* 	debug("exit\n"); */
 	return 0;
 }
 

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