When changing video timing dynamically via fbset the screen sporadically
is rendered black.

With the attached fix which disables VCO prior to timing register
change the problem disappears.

I had a look at the Xserver register setup code. Here the VCO is
disabled in the same way [1].

This patch is taken from vga-sync-field version 0.0.11 [2][3].

[1] 
http://cgit.freedesktop.org/xorg/driver/xf86-video-intel/tree/src/i830_driver.c
[2] http://lowbyte.de/vga-sync-fields/vga-sync-fields-0.0.11.tgz
[3] 
http://git.hellersdorfer-jugendchor.de/?p=vga2scart.git;a=commitdiff;h=dcc3b863e5a663652587619c357bd20075af6896

Signed-off-by: Thomas Hilber <spar...@lowbyte.de>
Signed-off-by: Paul Menzel <paulepan...@users.sourceforge.net>
CC: Dave Airlie <airl...@gmail.com>
---
 drivers/video/intelfb/intelfbdrv.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/video/intelfb/intelfbdrv.c 
b/drivers/video/intelfb/intelfbdrv.c
index 6d8e541..7ba8db5 100644
--- a/drivers/video/intelfb/intelfbdrv.c
+++ b/drivers/video/intelfb/intelfbdrv.c
@@ -1364,6 +1364,11 @@ static int intelfb_set_par(struct fb_info *info)
        DBG_MSG("intelfb_set_par (%dx%d-%d)\n", info->var.xres,
                info->var.yres, info->var.bits_per_pixel);
 
+       /*
+        * Disable VCO prior to timing register change.
+        */
+       OUTREG(DPLL_A, INREG(DPLL_A) & ~DPLL_VCO_ENABLE);
+
        intelfb_blank(FB_BLANK_POWERDOWN, info);
 
        if (ACCEL(dinfo, info))
-- 
1.6.2.4

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