[Bug 75345] [HD4600] DVI does not support dual-link

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75345

--- Comment #8 from Adam Nielsen <a.nielsen at shikadi.net> ---
Looks like you're right - I checked the specs, and a few weeks after I bought
the board the spec was updated to say the max DVI res was 1920x1200 at 60Hz.  I
wish they'd just supplied a couple of DP ports and a DVI adapter instead...

(In reply to comment #4)
> (Instead of adopting dual-link, Intel developed a higher bandwidth
> connector, DisplayPort - unfortunately the world has been slow jumping on
> the bandwagon.)

Ironically of my four screens, two of them support DisplayPort but I can't
connect them both via DP because the Intel motherboard doesn't provide enough
DP connectors!

(In reply to comment #5)
> IIUC dual-link DVI does not work with the Windows driver either (but I have
> no confirmation). I'm a bit on thin ice here, but I don't think increasing
> the HDMI frequency directly helps dual-link DVI unless there's some active
> components supporting dual-link. It depends on how the DVI port is set up I
> guess.

I guess this might affect the maximum resolution possible over single-link DVI,
but I believe this monitor will only sync with 1920x1200 at 60Hz over single-link,
so any bandwidth increases over the single link won't work.  I believe this
because there's a HDMI input but it only supports up to 1920x1200 at 60Hz.  I also
tried a modeline for 2560x1600 at 30Hz (native res, and refresh rate that just
fits within single-link's bandwidth) but the monitor came up saying the
vertical refresh was out of range.

> Adam, are you running at least kernel v3.11?

I'm running kernel 3.13.4, and last tested the dual-link under 3.12.

(In reply to comment #6)
> The other thing to remember is that the monitor will not advertise a
> dual-link mode to -intel (because it using the wrong connector). Therefore I
> feel reasonably confident that if it is in the EDID then we are pruning it,
> which should then be fixable by bumping our clock limits to the hw maximum.

At least under kernel 3.12 with the DVI-D dual-link cable, it was showing
2560x1600 at 60Hz as a valid mode and KMS was selecting it by default, resulting
in no picture shortly after boot.  I think the monitor is advertising all modes
and expecting the driver to prune it if dual-link is unavailable.

In summary, it looks like Chris is right and the hardware is not dual-link
capable.  So I guess the bug is that the driver attempts to set a dual-link
mode when it is not achievable.

I should add the DVI output is reported by KMS as a HDMI output, so perhaps
it's not possible to identify it as a DVI port and limit the bandwidth?  If
this is correct, then in theory one should be able to connect a HDMI 1.4
capable monitor (not mine) to the DVI port with a passive adapter, and get
2560x1600 at 60Hz.

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20140224/a6c1f8cf/attachment.html>