[Intel-gfx] [PATCH]i830_display.c:don't disable vga centering bit.

[Olivier Fourdan]

Olivier Fourdan said the following on 07/15/2009 11:58 AM:
> Ma Ling said the following on 02/05/2009 09:48 AM:
>  > commit id db9f5915ce812144ffd9d2aa42e8ba
>  > which resolved bug #17235, but generate new regression-bug #19715.
>  > This patch intends to resolve bug #17235, and avoid regression as well.
>  > We have successfully re-tested it for bug #17235 and #19715 respectively.
>
> Actually, I suspect commit db9f5915 has also introduced another
> regression when changing resolution with a VGA connected monitor,
> which is not addressed by the later commit cdcca959 and is still
> present in the latest of the 2.6 branch (2.6.3) apparently.
>
> Without the patch from db9f5915 (and following), changing resolutions
> with only VGA connected on a Q45/Q43 chipset works fine and reliably.
>
> However, with that patch applied, the monitor sometimes (roughly half
> of the time) goes out of sync after changing the resolution with
> xrandr and the display remains black.
>   
> [...]



Actually KMS seems to be immune to the problem. So comparing the code of 
i9xx_crtc_dpms() in intel_display.c in the kernel code with the one from 
its equivalent i830_crtc_dpms() in i830_display.c I see that the 
VGA_DISP_DISABLE is disabled no matter what in the kernel driver whereas 
in i830_disable_vga_plane() the function returns immediatly if the bit 
is already set:

The problem reported previously does not seem to occur with the attached 
patch.

Cheers,
Olivier.
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