[Intel-gfx] Mode setting not working with SandyBridge.

[Colin Alie]

Hello,

I have a HTPC with a Core i3-2120T with an Intel DH67GD motherboard.
I'm running Debian Wheezy/Sid.  Versions for key software on the system
are as follows.
- kernel: linux 3.1.0, 3.1.5, 3.2.0-rc6
- 3D driver:  mesa 7.11.1
- 2D driver:  xserver-xorg-video-intel 2.17.0
- libdrm:  libdrm-intel1 2.4.27
- xserver:  X.Org 1.11.2

When connected (via HDMI) to my Sony Wega TV, the display is normal
during POST, the GRUB menu, and the first few seconds of booting the OS.
Shortly thereafter, the screen goes dark with horizontal lines that
flicker lines.  If I use the boot parameter 'acpi=off', the video output
is fine albeit at the `normal' size of 80x25.

Video output from the HTPC is fine when connected (via HDMI) to my LG
246WHX monitor.

I have a Dell laptop with a GMA X3100 graphics core (GM965 chipset) and
I am able to successfully use with the TV (connected via HDMI).  Below
are the modes "probed for output" by the laptop; I've successfully used
the modes "1280x720" and "720x480" in the past:

Modeline "1280x720"x60.0   74.25  1280 1390 1430 1650  720 725 730 750
+hsync +vsync
Modeline "720x480"x59.9   27.00  720 736 798 858  480 489 495 525 -hsync
-vsync
Modeline "640x480"x60.0   25.20  640 656 752 800  480 490 492 525 -hsync
-vsync

My guess is that the graphics driver on the HTPC is attempting to use
timings that are incompatible with the TV.  Here's what I get when I
query the frame buffer --- note the `timings' line:

# fbset -i

mode "1280x720"
    geometry 1280 720 1280 720 32
    timings 0 0 0 0 0 0 0
    accel true
    rgba 8/16,8/8,8/0,0/0
endmode

Frame buffer device information:
    Name        : inteldrmfb
    Address     : 0xe0063000
    Size        : 3686400
    Type        : PACKED PIXELS
    Visual      : TRUECOLOR
    XPanStep    : 1
    YPanStep    : 1
    YWrapStep   : 0
    LineLength  : 5120
    Accelerator : No

I tried to specify the device timings myself using fbset but it doesn't
seem like one is able to change the timings after they have already been
set?

# fbset -fb /dev/fb0 -pixclock 13468 -left 220 -right 110 -upper 20
-lower 5 -hslen 40 -vslen 5 -hsync high -vsync high

ioctl FBIOPUT_VSCREENINFO: Invalid argument

I'm looking to help troubleshoot and hopefully fix this problem as best
as I can.  Can anyone confirm the cause of the problem?  Assuming that
the problem is with incompatible mode setting, in the interim, is it
possible, say via a boot parameter, to specify the mode that the video
driver would use?  Thanks.

Until next time, Colin.