[Intel-gfx] limiting modes on 4k monitors on Haswell ULT

[Daniel Vetter]

On Thu, Oct 02, 2014 at 01:30:48PM +1000, Dave Airlie wrote:
> Hey guys,
> 
> so I have a haswell ULT laptop (lenovo t440s), and got access to a
> Samsung single panel 4k monitor (no MST).
> 
> Now we detect the monitor fine, but unfortunately the ULT hsw can't
> run it over DP, as it has clock limits in place. However we still
> offer the 60hz mode and we pick it by default, ensuing black screens.
> 
> I've tested the same monitor with a haswell in a t540p and it works
> fine due to having the higher limits in place.

We have the IS_HSW_ULX check in intel_dp_max_link_bw, and that's used by
both compute_config and mode_valid. So it should work, and from a quick
look I don't see any bugs. But obviously something is busted.

Can you please printk-augment intel_dp_mode_valid and check what's going
wrong there?

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch