[Bug 95476] New: [BXT-P] i915 driver overwrites the DDI PHY register for the 1366x78 panel with incorrect values

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95476

            Bug ID: 95476
           Summary: [BXT-P] i915 driver overwrites the DDI PHY register
                    for the 1366x78 panel with incorrect values
           Product: DRI
           Version: DRI git
          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: tarun.vyas at intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 123891
  --> https://bugs.freedesktop.org/attachment.cgi?id=123891&action=edit
Full dmesg log

In the APL platforms, the firmware enables the 1366x768 panels by correctly
programming the DDI PHY registers, but this leads to a PHY state mismatch
according to the i915 driver because the driver expects to read a value from
the PHY registers that differs from what was programmed by the firmware. Hence,
the i915 driver goes ahead and reprograms the PHY, incorrectly, causing the DP
link training to fail. The i915 driver will need modifications to correct this
behavior. Filing this bug to track those modifications.

Steps to reproduce:
1. Connect a 1366x768 panel as an eDP to a APL system.
2. Boot the system with dinq kernel.
3. The 1366x768 panel will fail to come up.

Reproduciblity: 100%

System architecture: x86_64

Kernel version: 4.6.0-01610-g68c6a6d-dirty

Linux distro: Chromium OS

Display Connector: eDP

Machine info:

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