[Bug 97013] New: VGA detection fails Intel i915

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97013

            Bug ID: 97013
           Summary: VGA detection fails Intel i915
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: ben.antin at endlessm.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 125185
  --> https://bugs.freedesktop.org/attachment.cgi?id=125185&action=edit
dmesg output from X441SA w/VGA connected

- system architecture: x86_64
- kernel version: 4.4.0
- Linux distribution: Ubuntu
- Machine or mother board model: Asus X441SA Braswell (Valleyview)
- Display connector: VGA

The driver fails to recognize an attached VGA port. On this particular SoC, it
appears that VGA is connected to a displayPort via an adapter. As far as I
know, this problem is specific to the Asus X441SA, as the X540SA correctly
recognizes the displayPort.

Comparing output of dmesg between Asus X540SA and X441SA reveals that the
displayPort for VGA output is connected to Port B:

[    2.908763] [drm:intel_dp_init_connector] Adding DP connector on port B
[    2.908853] [drm:intel_dp_aux_init] registering DPDDC-B bus for card0-DP-1

There is no mention of DP-1 on the logs from the X441SA.

Adding some print statements it seems that the following line is executed on
the X540SA but not on the X541SA:

_________________________
if (I915_READ(VLV_DP_B) & DP_DETECTED ||
       intel_dp_is_edp(dev, PORT_B))
                        intel_dp_init(dev, VLV_DP_B, PORT_B);
__________________________

This is from drivers/gpu/drm/i915/intel_display.c

It seems that the I915_READ() bit is 1 on the X540SA but 0 on the X441SA.
This seems somewhat similar to
https://bugs.freedesktop.org/show_bug.cgi?id=96321

Full dmesg output attached for X441SA.

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