[PATCH] SVGATextMode fix

Fix bug 5441.

I didn't know about messy programs like svgatextmode...  Couldn't this be
integrated in some linux/drivers/video/console/svgacon.c ?...  So because
of the existence of the svgatextmode program, the kernel is not supposed to
touch to CRT_OVERFLOW/SYNC_END/DISP/DISP_END/OFFSET ?

Disabling the check in vgacon_resize() might help indeed, but I'm really
not sure whether it will work for any chipset: in my patch, CRT registers
are set at each console switch, since stty rows/cols apply to consoles
separately...

The attached solution is to keep the test, but if it fails, we assume that
the caller knows what it does (i.e.  it is svgatextmode) and then disable
any further call to vgacon_doresize.  Svgatextmode is usually used to
_expand_ the display, not to shrink it.  And it is harmless in the case of
a too big stty rows/cols: the display will just be cropped.  I tested it on
my laptop, and it works fine with svgatextmode.

A better solution would be that svgatextmode explicitely tells the kernel
not to care about video timing, but for this an interface needs be defined
and svgatextmode be patched.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/video/console/vgacon.c

@@ -565,7 +565,11 @@ static int vgacon_switch(struct vc_data *c)
 		scr_memcpyw((u16 *) c->vc_origin, (u16 *) c->vc_screenbuf,
 			    c->vc_screenbuf_size > vga_vram_size ?
 				vga_vram_size : c->vc_screenbuf_size);
-		vgacon_doresize(c, c->vc_cols, c->vc_rows);
+		if (!(vga_video_num_columns % 2) &&
+		    vga_video_num_columns <= ORIG_VIDEO_COLS &&
+		    vga_video_num_lines <= (ORIG_VIDEO_LINES *
+			vga_default_font_height) / c->vc_font.height)
+			vgacon_doresize(c, c->vc_cols, c->vc_rows);
 	}
 
 	return 0;		/* Redrawing not needed */
@@ -1023,7 +1027,8 @@ static int vgacon_resize(struct vc_data *c, unsigned int width,
 	if (width % 2 || width > ORIG_VIDEO_COLS ||
 	    height > (ORIG_VIDEO_LINES * vga_default_font_height)/
 	    c->vc_font.height)
-		return -EINVAL;
+		/* let svgatextmode tinker with video timings */
+		return 0;
 
 	if (CON_IS_VISIBLE(c) && !vga_is_gfx) /* who knows */
 		vgacon_doresize(c, width, height);