[Bug 105534] amdgpu cannot set 2560x1440 at 60 mode even though monitor,gpu and motherboard support it

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105534

--- Comment #5 from Alex Deucher <alexdeucher at gmail.com> ---
(In reply to Christian König from comment #3)
> What you can use is either an active DP to dual DVI converter (probably
> rather expensive if such a thing even exists) or native DP/HDMI (if the
> monitor has connectors for that).

They are actually relatively common for just these sorts of scenarios.  Not
sure about cost however.

(In reply to philipmorant from comment #4)
> Thanks for replies. My monitor is DVI DL only.
> 
> My old Haswell i5 4670 with HD4600 graphics was also single link DVI only
> (https://communities.intel.com/thread/44135), and it worked at 60Hz. Could
> somebody please explain why haswell can do it but raven can't ?

I'm not sure how the intel hw is designed.  I can't comment on exactly what is
happening.  I suspect what is happening is that the intel driver is not
validating the link requirements and treating the DVI port like HDMI and
sending the high bandwidth mode over a single TMDS link.  The monitor just
happens to accept it.

> 
> Otherwise I find myself assuming that the hardware is capable of DL DVI,
> just that the manufacturers aren't validating for it, ergo fixable in
> software.

No.  DL DVI requires two digital transmitters, one for each TMDS link.  We only
wire a single transmitter to each physical connector.  For DL DVI, you need two
transmitters connected to the physical connector.

> 
> I understand if AMD object to coding for something that hasn't been
> validated (I'd do the same myself).  Would it be possible alternatively to
> provide hints in log output or code comments or on a wiki somewhere, such
> that people in my position can hack the source themselves ?

You could try hacking the driver to treat the monitor as HDMI even through it's
DL DVI.  Maybe your monitor will accept the timing over a single TMDS link.

> 
> Secondly, even accepting the single link limitation, shouldn't it be
> possible to run at 33 refresh rate ?  I tried at 30 and got nothing.
> 

It depends on the hardware and the panel in the monitor.  The monitor hardware
may not like 30 Hz refresh rates.  

> Thirdly, why does amdgpu refer to the connection as HDMI-A-3 ?  There's no
> HDMI in the setup at all.

The display connectors are read from a table in the bios and are determined by
the OEM that designs the board.  It our case the OEM seems to have set it up as
3 HDMI connectors and a DP connector.  What physical connectors are actually on
the board?

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