Not able to reproduce this issue on build 9325.0.0
I can change the external display resolution.


Note: Only HD display devices supports 4K resolution.

Thank you for your reply.

Unfortunately I am still able to reproduce this issue with the Medion AKOYA S2013 und the Dell UP3214Q connected over HDMI.

From your reply “I can change the external display resolution.” I think, you might have misunderstood my problem. I am able to change resolution from the *presented* list. But the list is incomplete, as my display supports higher resolutions than 1920 px x 1200 px, and since HDMI 1.4 3840 px x 2160 px is supported [1].

1.  As you cannot reproduce the issue, I am understanding you correctly, that you were able to drive your external display connected over HDMI with 4K resolution?
2.  What device (Chromebook and monitor) did you use for testing?
3.  Where do you get your build from? From *Plattform*? I am tested with version 56.0.2924.110 and Plattform 9000.91.0.

I kindly ask you to reopen the issue.


[1] https://en.wikipedia.org/wiki/HDMI#Version_comparison

veyron_jaq does not support 4K external display resolution.

There is a patch to enable that [1].

According to the developers there were problems though.

From the Chromium OS developers:

> I'm pretty sure you're out of luck because IIRC we couldn't get the PLLs
> jitter-free enough to support that bit rate. Fievel might be a different story 
> because it doesn't need to drive an internal display at the same time. Even if 
> you managed to get it working, there's a good chance the CPU and memory
> bandwidth would make it uncomfortable.

> Yup, out of luck for 4k on rk3288 devices.  As XXX says, possibly fievel
> or tiger might have the hardware changes to be jitter free enough, but it's
> not a great experience.  If you wanted to build your own kernel, you can
> theoretically enable 4K that might work on some monitors, but it is out of
> spec and doesn't work everywhere.

The associated bug report [2] is unfortunately locked for “outsiders”.

[1] https://chromium-review.googlesource.com/c/388393/
[2] https://code.google.com/p/chrome-os-partner/issues/detail?id=59162

Just because the chip supports 4K doesn't mean the board does.  Nothing on the veyron spec claims 4K is supported on this laptop.

If you happen to not care about being 100% compatible with all 4K monitors and happen to be the kind of person who wants to install his/her own kernel (and forgo auto updates), you could in theory revert:

https://chromium-review.googlesource.com/c/301573/

It won't work perfectly but certainly some 4K monitors seemed to work even with the out of spec signaling.


It is remotely possible that there might be some way to adjust all the parameters of the rk3288 HDMI PHY to make 4K within spec, but those parameters are largely undocumented to me and I'm also not an expert on HDMI signaling.  Also note that there is a certain amount of board-to-board variance here, so to ship something out to everyone we'd either need to get the signaling in spec with a wide margin or test across a large number of boards.

I spent massive amounts of time getting veyron products able to reliably support a wide range of pixel clocks on HDMI, so hopefully you're at least enjoying the fact that you can get all the resolution that you have today.  All other rk3288-based kernels that I'm aware of only support "HDMI" type clock rates and note "DVI" type clock rates, so on many monitors you end up at a much worse resolution than you do in the Chrome OS kernel.