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

Daniel Vetter daniel at ffwll.ch
Sun Jan 22 11:40:11 CET 2012

On Sun, Jan 22, 2012 at 02:55, Alfonso Fiore <alfonso.fiore at gmail.com> wrote:
> On Sat, Jan 21, 2012 at 10:09 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>> Ok, from the above it looks like the VGA input on your TV is dirt-cheap
>> and it barely manages to sync at 800x600 and fails already at 1024x768 -
>> not even the bios manages to put a picture on your TV :(
>> To make sure that this is not an issue with the intel gpu, can you maybe
>> test the vga input with another machine with different gpu?
> Hi Daniel,
> I used this TV for the last 3 years connecting each and all my laptops
> and I never had a problem running 1024x768 with Windows over VGA (as
> an extension of my laptop).
> However cheap my VGA input might be, Windows handles it just fine.
> My current GPU is ATI mobility radeon HD 3400.
> If you want, I can try to run Ubuntu from USB on my laptop and see if
> Ubuntu can control my monitor over VGA.
> Let me know if this test helps at all (I would prefer to skip it if
> the info I provided are enough).
> I don't have other desktops.
> The only box I can try for POST over VGA is an ALIX
> (http://pcengines.ch/) and it also doesn't work very well with my TV
> but at least it shows a flickering image.
> Again, with laptops and Windows it has been running fine for ages over VGA.

Ok, so we can't blame the TV ;-)

> Also: I'm sure you are looking at the big picture, but my goal is for
> sure HDMI, not VGA.
>> The overscan is expected because your other output HDMI is still at
>> 1024x768 and hence your desktop is large enough to fit both.
>> See the first line starting with "Screen 0:" in the xrandr output for
>> current the size of your desktop.
> gotcha. Thanks. I didn't know that (but I could have thought about it...)
>> Yep, excellent test descriptions! I still need to look at the register
>> dumps, but I think another test might be useful:
>> Only HDMI with nomodeset, then again grab the intel_reg_dump. Iirc that
>> works, so it could be useful to see how the bios sets things up with just
>> the hdmi cable.
> is there a typo? Or maybe I don't understand what you are asking?
> "grab the intel_reg_dump. Iirc that works" ????
> is that intel_reg_dumper?
> So you want me to run the same script over HDMI (with only HDMI cable)
> with nomeset with all the available resolutions?

Actually I only need the output of intel_reg_dumper, resolution
doesn't really matter that much. It just needs to be a HDMI-only
configuration that works.

>> Another thing to try with VGA is whether the higher refresh-rate helps.
>> You can select that with --rate, i.e.
>> xrandr --output VGA1 --mode 1024x768 --rate 60.0
> Should I try just with 60? Or also with other values?
> Is this test with or without nomodeset (I guess w/o, but better check)?
> Only VGA cable? or also HDMI connected? or both cases?
> Please detail case conditions.

Test with the i915 driver (i.e. no nomodeset on the kernel cmdline),
if you want you can try both VGA cable only and VGA/HDMI but it
shouldn't matter. xrandr -q output shows only 55.4 and 60.0 for this
resolution, so I think it doesn't make sense to test anything else.

Yours, Daniel
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch

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