[Nouveau] HDMI pixel clock limits

[Ilia Mirkin]

In the meanwhile we're pushing out a change that just blanket allows
225MHz on Fermi and 297MHz on Kepler, with a kernel option override
available. At least one GF106 user claims to have working 297MHz with
proprietary drivers (and with nouveau in presence of the patches):

https://bugs.freedesktop.org/show_bug.cgi?id=91236

Having an accurate way to auto-detect this would be ideal though, as
higher bandwidth monitors are becoming more ubiquitous.

  -ilia


On Mon, Oct 26, 2015 at 1:35 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> Hello,
>
> Various HDMI versions enable higher and higher pixel clocks. However
> individual GPUs are not required to support the maximum pixel clock
> supported by the spec in order to be compliant. It appears that some
> GPUs max out at 225MHz while others at 297MHz (while others still, I
> assume, are limited to 165MHz, esp among the older ones).
>
> We've been unable to find this in the VBIOS (I had a thought that it
> was in the table pointed to by the 'T' table, but we have a
> counterexample to that). Could you suggest a way to find this
> information either from the VBIOS or based on the GPU? Are there
> differences between regular HDMI and DP -> HDMI (passive)?
>
> This is becoming more and more relevant as 2560x1440/3840x2160
> displays are become more common, while (dual-link) DVI-D is on its way
> out.
>
> Thanks,
>
>   -ilia