[Intel-gfx] PROBLEM: i915 Haswell KMS wrong maximum resolution

[Dave Airlie]

On Mon, Mar 31, 2014 at 5:43 PM, Jani Nikula
<jani.nikula at linux.intel.com> wrote:
> On Sun, 30 Mar 2014, Kenneth de Mello <kdemello1980 at gmail.com> wrote:
>> What about dual-link DVI?   I though the additional link addressed the
>> pixel clock limitation.   Has it only been using a single link this entire
>> time, and it's only worked by ignoring the maximum dotclock, so in other
>> words, the fact it works at all is the bug?
>>
>> Also, the commit that rejects mode exceeding 165MHz states:
>>
>>     "Single-link DVI max dotclock is 165MHz. Filter out modes with higher
>>      dotclock when the monitor doesn't support HDMI."
>>
>> Does this mean HDMI in general?   This monitor does support HDMI, but the
>> maximum resolution when using the physical HDMI ports is 1920x1080.
>>
>> What is the solution here, to switch to displayport if I want to use kernel
>> 3.13.7 and beyond?   (This is fine, I just need to know so I can buy the
>> cable).
>
> For further details please see the bug report [1].
>
> The reason for the change was that modes with higher than 165 MHz
> dotclock are invalid for single-link DVI. We don't support dual-link DVI
> natively. Thus this is about HDMI->DVI adapters which are either
> dual-link DVI (Ville says highly unlikely) or single-link DVI that allow
> higher than 165 MHz dotclock in the monitor end. I'm not sure how we
> could distinguish that from a regular single-link DVI that *is* bound by
> the maximum dotclock.
>
> Product details for the adapter you're using might be interesting.

DVI->HDMI adapters are just wires.

If you plug a HDMI monitor via one of those and the hw can do HDMI
speed single links it should work in theory, since the EDID would show
a HDMI monitor.

The DVI limitations are actually the cables rather than the connectors
from what I understand, but I could be misinformed.

Dave.