[Bug 107503] New: Native screen resolution not working correctly over HDMI LSPCON (i915)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107503

            Bug ID: 107503
           Summary: Native screen resolution not working correctly over
                    HDMI LSPCON (i915)
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: nicholas.stommel at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

When booting Fedora, Ubuntu, OpenSUSE, and really any distribution running
Linux kernel 4.16 and above, the Intel integrated graphics card (in my case the
Kabylake HD 630) does not correctly enable the connected monitor's native
resolution over HDMI on LSPCON. Any kernel 4.15 and below does not cause this
issue. This issue is currently confirmed but lacks an actual kernel bug report
on the Redhat bugzilla here:
https://bugzilla.redhat.com/show_bug.cgi?id=1570392

dmesg logs show: 
[drm:intel_dp_get_link_train_fallback_values [i915]] *ERROR* Link Training
Unsuccessful 

Followed by reapeating lines of:
[drm:lspcon_wait_mode [i915]] *ERROR* LSPCON mode hasn't settled 

In particular, 1280x1800 and 1680x1050 are the two resolutions I find myself
limited to when the kernel boots and doesn't correctly use the full 1920x1080
native resolution of the monitor (in this case, a Samsung CF591). This issue
does not, however, appear related to this particular monitor as two others I
have tried end up with the same issue. Nor is it a cable problem, I switched
that out several times as well. After much testing, the issue seems very
non-deterministic and fairly random indeed. Grub and Plymouth don't appear to
be culprits either.

Basically, the kernel isn't correctly setting full HD resolution of the monitor
around *half* the time. Booting Fedora 28 or Ubuntu 18.04 with kernel version
4.16 or newer on my machine with Intel graphics using the HDMI LSPCON connector
is like tossing a die: I either get Full HD, those two variants of stretched
and incorrect low resolution, or (rarely, but still) failure to boot at all. 

After some confusion, I determined that the HDMI option board on the system
motherboard of the HP Elitedesk 800 G3 DM is, in fact, using an LSPCON
converter from DP->HDMI using this helpful info from Intel i915 dev Imre Deak:
"There are two ways to connect HDMI to the APL RVPs: via the DDI1 DP++ plug
with an DP->HDMI dongle, or via the DDI0 HDMI plug which is connected to the
SoC through the LSPCON converter. You seem to be using the second scenario with
LSPCON being in the protocol converter mode (configured as such by BIOS). In
that case the connection will show up as a DP connector." 

Other users on machines including Intel NUCs have confirmed this issue with
HDMI over LSPCON resulting in incorrect resolution on boot. It appears a
regression occurred in LSPCON handling through kernel 4.16 and above.

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