i915 driver limits virtual resolution to 8192x8192

[Jelle De Loecker]

I have an Intel Iris Pro 580 in my Intel Skull Canyon NUC6I7KYK, a nice little device that has 3 video outputs:

* HDMI 2.0
* Mini DisplayPort
* Thunderbolt USB-C

The product specifications states that the device is able to output three 4K signals. Unfortunately, whenever I tried this in Ubuntu it failed, without any clear error message.

After fiddling with other DEs, Kubuntu told me the virtual resolution was not supported. And indeed, as soon as I limited the virtual resolution of the 3 screens to fit in 8192x8192 pixels, all screens worked.

Apparently, the i915 driver (in "drivers/gpu/drm/i915/intel_display.c") has not been updated for newer devices when reporting the maximum resolution.

As you can see here: https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/i915/intel_display.c#L14671

Only GEN_2 & GEN_3 are checked for, but since the 7th generation max virtual resolutions of 16384x16384 are supported.

This issue has been reported to the i915 maintainers a few times, but nothing has changed yet :/

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1774425

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Joseph Salisbury (jsalisbury)]

Did this issue start happening after an update/upgrade? Was there a prior kernel version where you were not having this particular problem?

Would it be possible for you to test the latest upstream kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.17 kernel[0].

If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as "Confirmed".

Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.17-rc7

[Dan Kegel (dank)]

See also similar bugs
https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1776260
https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1714178

Those were treated as if the 8kx8k limit was ok, and the bug was in the compositor
which failed to work around that limit. Perhaps this bug could be for the
lack of the raised limit when using 7th generation chips, if the limit is really
higher there?

[Dan Kegel (dank)]

https://lkml.org/lkml/2017/12/7/201 tries to raise the limit, but according to
https://bugs.freedesktop.org/show_bug.cgi?id=102508#c11 it does not work.

Also, Skull Canyon is 6th generation, is it not? See https://www.intel.com/content/www/us/en/nuc/nuc-kit-nuc6i7kyk-features-configurations.html