[Intel-gfx] Sandy Bridge Desktop - 1920x1080i interlace not working

Alfonso Fiore alfonso.fiore at gmail.com
Fri Jan 20 00:37:25 CET 2012

On Thu, Jan 19, 2012 at 9:50 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> Ok, please make this _really_ precise, we need to know exactly when things
> work and when not. I presume this was showing a perfect screen over the
> HDMI cable?

Yes, I was referring to HDMI. In fact, I was never able to see anything over VGA
with this MB + CPU (I never tried VGA with H55 + i3 550 cause HDMI worked
but I used VGA from my laptop with the same cable and the same TV).
Interestingly, I can always see BIOS and BIOS menu over HDMI
but when I connect only VGA I can't see anything also at the BIOS level.
So maybe the VGA problem has nothing to do with the driver?
[I was wrong, I managed to see something over VGA during these tests]

I'll try to be as precise as I can.

so I created a little script that I will run at each test.

$ cat run_me.sh
WHEN="`date +%Y%m%d_%H%M%S`"
xrandr -q > ./xrand-q.$WHEN.output
xrandr --verbose > ./xrand--verbose.$WHEN.output
dmesg > ./dmesg.$WHEN.output
cp /var/log/Xorg.0.log ./Xorg.0.$WHEN.output
cp /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-VGA-1/edid
cp /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-HDMI-A-2/edid
> ./intel_reg_dumper.$WHEN.output

And attached you can find the whole tgz. Here I simply walk you
through my tests.

Only VGA (DVI-I) connected.
Changing TV source to VGA.
Nothing shows on the screen (not even BIOS).
But LightDM started (I can connect with VNC).

NO reboot
NO cable change (Only VGA (DVI-I) connected and TV source to VGA)
xrandr --output VGA1 --mode 800x600 (from VNC)
well... amazing. I can see the screen. I get no overscan left/right
but a bit up/down

connecting both VGA and HDMI
TV source still on VGA so I don't see anything (blue screen)
connecting over VNC I can see screen is 1024x768

NO reboot
NO cable change
NO TV source change
xrandr --output VGA1 --mode 800x600 (from VNC)
the screen goes from blue to the actual desktop,
but the TV shows 800x600 while the resolution stays at 1024x768
so there is huge overscan at bottom and right plus a bit on the top.
since you said "Please ensure that you use the same resolution for both"
(but I have a feeling I didn't understand you)
I'll put this back to 1024x768 before running tests on HDMI
xrandr --output VGA1 --mode 1024x768 (from VNC)
the screen goes back to blue

NO reboot
NO cable change
TV source change from TV to HDMI
the screen is as expected perfect with not a pixel of overscan

NO reboot
NO cable change
NO TV source change
xrandr --output HDMI2 --mode 1280x720 (from VNC)
the screen shows but with overscan on all four edges

NO reboot
NO cable change
NO TV source change
xrandr --output HDMI2 --mode 800x600 (from VNC)
this is similar to what happened over VGA:
the desktop stays 1024x768 but the TV only shows 800x600
so huge overscan bottom and right
when I removed the VGA cable for the next tests the screen
automatically switched to 1024x768
I run the script again just in case it gives you some good info:

connecting only HDMI
login screen is "weird" (I sent the photo already)
Ah, I didn't realize this earlier! From VNC I see that
lightDM is running at 1280x720 when it looks "weird"
when I type my password the screen goes to 1024x768 and now it's black
(used to be cut in half)

NO reboot
NO cable change
NO TV source change
xrandr --output HDMI2 --mode 1280x720 (from VNC)
weird! The screen stays black (so it doesn't look like the login screen)
the desktop (from VNC) correctly resizes to 1280x720

NO reboot
NO cable change
NO TV source change
xrandr --output HDMI2 --mode 800x600 (from VNC)
black screen
the desktop (from VNC) correctly resizes to 800x600

I believe I follow your instructions on what info to give you.

I hope this will help you trace the bug.


> Also please recheck for the split-screen issue whether that is some custom
> mode still lingering around by pasting xrandr -q output. For the broken
> case (i.e. only HDMI connected) also please try to change the resolution
> to something else like 1024x768 and see what happens.
> I suspect you've had the other output still on with 1024x768. You can
> always double-check with xrandr, '*' marks the currently active mode (and
> at the top of each output you see which part of a possibly large desktop
> it scans out).

> A few other things to test.
> - Check whether the edid changes when you connect only one cable. Yep,
>  that can happen.
> - Check what happens when you only connect the VGA cable.
> - There's likely something broken within our driver if HDMI+VGA works, but
>  HDMI alone not. The kernel/X also switch on the VGA output which might
>  influence (but shouldn't) how we set up HDMI. To check that out please:
> Attach xrandr --verbose output for both configurations. Please ensure that
> you use the same resolution for both, i.e. for the HDMI+VGA case switch to
> 1280x720 for the HDMI output.
> Grab intel-gpu-tools v1.1 (hopefully your distro ships it) and run the
> intel_reg_dumper tool for both configurations (again, please ensure you
> use the same mode for HDMI and that you don't change anything between
> grabbing the xrandr output and the intel_reg_dumper output).
> Yours, Daniel
> --
> Daniel Vetter
> Mail: daniel at ffwll.ch
> Mobile: +41 (0)79 365 57 48
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