[Bug 94087] New: eDP panel exhibits sparse random noise and flickering (link issue), forcing DP DDI profile helps [Lenovo T450s]

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94087

            Bug ID: 94087
           Summary: eDP panel exhibits sparse random noise and flickering
                    (link issue), forcing DP DDI profile helps [Lenovo
                    T450s]
           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: alex at alexanderweb.de
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: ben at bwidawsk.net, intel-gfx-bugs at lists.freedesktop.org
     i915 features: display/eDP

Created attachment 121659
  --> https://bugs.freedesktop.org/attachment.cgi?id=121659&action=edit
DDI profile switch from eDP to DP by ben at bwidawsk.net

The internal eDP panel of my recently bought Lenovo Thinkpad T450s exhibits
sparse random noise and flickering (link issue). The CPU is i5200U (Broadwell).

Video of the symptom: http://ghostbusters.alexanderweb.de/t450s.mov

Ben and I discovered that forcing the DP DDI profile works around the problem.
See the patch by Ben (ben at bwidawsk.net) that I attached.

Ben suspects the vswing to be incorrectly inferred from VBT.

Found on Kernel 4.2.0-27-generic, also affected: 4.4.1-vanilla.

Suggested fixes by Ben:
 - Check whether VBT is correctly read and/or whether it is faulty.
 - Either:
  - Provide a vswing override that works on BDW (edp_vswing does not)
    - Optionally contact Lenovo to fix the T450(s) BIOS (current one used:
JBET55WW, 1.20) to have a correct VBT.
  - Or: Fix VBT parsing.

Kernel params used:
 - Setting "i915.enable_ips=0 i915.modeset=1 i915.lvds_use_ssc=0" does not
change the behaviour.

Kernel messages related to VBT:

[drm:validate_vbt] Using VBT from OpRegion: $VBT HASWELL        d
[drm:parse_general_features] BDB_GENERAL_FEATURES int_tv_support 0
int_crt_support 0 lvds_use_ssc 1 lvds_ssc_freq 120000 display_clock_mode 0
fdi_rx_polarity_inverted 0
[drm:parse_general_definitions] crt_ddc_bus_pin: 0
[drm:parse_lfp_panel_data] DRRS supported mode is static
[drm:parse_lfp_panel_data] Found panel mode in BIOS VBT tables:
[drm:drm_mode_debug_printmodeline] Modeline 0:"1920x1080" 0 141000 1920 1936
1952 2104 1080 1083 1097 1116 0x8 0xa
[drm:parse_lfp_panel_data] VBT initial LVDS value 30033c
[drm:parse_lfp_backlight] VBT backlight PWM modulation frequency 220 Hz, active
high, min brightness 3, level 255
[drm:parse_sdvo_panel_data] Found SDVO panel mode in BIOS VBT tables:
[drm:drm_mode_debug_printmodeline] Modeline 0:"1600x1200" 0 162000 1600 1664
1856 2160 1200 1201 1204 1250 0x8 0xa
[drm:parse_sdvo_device_mapping] No SDVO device info is found in VBT
[drm:parse_driver_features] DRRS State Enabled:1
[drm:parse_ddi_port] Port A VBT info: DP:1 HDMI:0 DVI:0 EDP:1 CRT:0
[drm:parse_ddi_port] VBT HDMI level shift for port A: 0
[drm:parse_ddi_port] Port B VBT info: DP:1 HDMI:1 DVI:1 EDP:0 CRT:0
[drm:parse_ddi_port] VBT HDMI level shift for port B: 2
[drm:parse_ddi_port] Port C VBT info: DP:1 HDMI:1 DVI:1 EDP:0 CRT:0
[drm:parse_ddi_port] VBT HDMI level shift for port C: 13
[drm:intel_dsm_pci_probe] no _DSM method for intel device
[drm:i915_gem_init_stolen] Memory reserved for graphics device: 32768K, usable:
31744K
[drm:intel_power_well_enable] enabling always-on

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