[PATCH] fix fixed-mode framebuffer devices with X 1.4.2

This patch fixes the problem with Xorg 1.4.2 not starting when run
on framebuffer drivers which do not support mode-setting.
The corresponding Xorg bug is:
https://bugs.freedesktop.org/show_bug.cgi?id=17153 

The solution is, that we just simply fill in a "emulated" valid
monitor/modeline for fixed mode devices (aka drivers which don't
implement fb_check_var) into the "var" struct during the
register_framebuffer() initialization call. Since we fill in a
valid monitor/modeline, X will not have any problems with it.

The patch has a few benefits:
a) It keeps binary compatability/behaviour for FBIOGET_VSCREENINFO and
   FBIOPUT_VSCREENINFO.
b) In Xorg.conf files, users can simply delete all monitor and display
   sections -> Xorg will autoconfigure itself to the only valid resolution/
   modeline itself on all fixed mode devices.


Signed-off-by: Helge Deller <deller@gmx.de>
CC: Geert Uytterhoeven <geert@linux-m68k.org>
CC: Ville Syrjälä <syrjala@sci.fi>
CC: Michel Dänzer <redacted>

diffstat:
 fbmem.c |   16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 98843c2..1e9a4ad 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c

@@ -1470,9 +1470,23 @@ register_framebuffer(struct fb_info *fb_info)
 	if (!fb_info->pixmap.blit_y)
 		fb_info->pixmap.blit_y = ~(u32)0;
 
-	if (!fb_info->modelist.prev || !fb_info->modelist.next)
+	if (!fb_info->modelist.prev || !fb_info->modelist.next) {
 		INIT_LIST_HEAD(&fb_info->modelist);
 
+		/* Initialize an emulated modeline for drivers which
+		 * do not support mode setting. */
+		if (!fb_info->fbops->fb_check_var &&
+		     fb_info->var.pixclock == 0) {
+			char modestr[32];
+			snprintf(modestr, sizeof(modestr), "%dx%d-%d",
+				fb_info->var.xres,
+				fb_info->var.yres,
+				fb_info->var.bits_per_pixel);
+			fb_find_mode(&fb_info->var, fb_info, modestr,
+				NULL, 0, NULL, fb_info->var.bits_per_pixel);
+		}
+	}
+
 	fb_var_to_videomode(&mode, &fb_info->var);
 	fb_add_videomode(&mode, &fb_info->modelist);
 	registered_fb[i] = fb_info;

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