[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 #6 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Alex Deucher from comment #5)
> (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.

FYI in i915 we validate everything when enumerating the modes, but during a
modeset we allow the user mode to exceed the DP++ dongle and sink limitations
for just these sort of cases (source limitations we enforce always). The user
has manually added the out-of-spec mode so presumably they know what they're
doing...

Also we can't reliably tell what kind of connector is present on the board so
we treat DVI and HDMI the same. DP++ we treat a little special because we can't
actually read out the state of the CONFIG1 pin so we can't tell whether a type1
DVI DP++ dongle is present or not. So if we can't read out the dongle registers
and the connector *looks* like a DP++ in the video BIOS tables we assume the
dongle to be present. But again the user can still override this by forcing an
out-of-spec mode.

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