[Bug 96923] New: Black display once loading the module i915 on Bay trail (DSI/MIPI) - Zen10 tablet

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96923

            Bug ID: 96923
           Summary: Black display once loading the module i915 on Bay
                    trail (DSI/MIPI) - Zen10 tablet
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: viric at viric.name
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 125061
  --> https://bugs.freedesktop.org/attachment.cgi?id=125061&action=edit
The i915_vbt debugfs dump

After fixing the PWM backlight of this LPSS system (bug 96571), I get a black
screen once I load the i915 module. Before it, (efi fb), it displays fine.

I'm using Shobhit patches for enabling the PWM plus another one in the referred
bug, over 4.5 and 4.6.3, with the same outcome: backlight works great, the
pixels get all black after a quick flicker at module loading.

I notice from the drm debugfs that the lcd panel is connected with DSI. The LCD
panel, acording to the BIOS setting for "MIPI panel", is an "Innolux 8x12"
(10.1", 800x1280) like this:

http://www.innolux.com/Pages/Dyn/Product3_EN.aspx?cateN=Tablet%20Hybrid%20Solution&catedes=Tablet/Hybrid%20Solution&catel1=Tablet&catel2=WXGA&size=10.1"&Language=EN

The i915 module does not seem to know an EDID for the panel, but has a VBT that
I will attach.

The dmesg content at the time of i915 loading is this:

[   72.226417] Linux agpgart interface v0.103
[   72.265453] [drm] Initialized drm 1.1.0 20060810
[   72.384656] [drm] Memory usable by graphics device = 2048M
[   72.384666] checking generic (80000000 1d5000) vs hw (80000000 10000000)
[   72.384669] fb: switching to inteldrmfb from EFI VGA
[   72.384773] Console: switching to colour dummy device 80x25
[   72.384904] [drm] Replacing VGA console driver
[   72.385680] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[   72.385686] [drm] Driver supports precise vblank timestamp query.
[   72.407090] vgaarb: device changed decodes:
PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[   72.465860] ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
[   72.466436] input: Video Bus as
/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input6
[   72.466663] [drm] Initialized i915 1.6.0 20160229 for 0000:00:02.0 on minor
0
[   72.508911] audit: type=1130 audit(1468319461.361:75): pid=1 uid=0
auid=4294967295 ses=4294967295
msg='unit=systemd-backlight at backlight:intel_backlight comm="systemd"
exe="/nix/store/24qss832pv2xwpjbzk354kimypf4f1jc-systemd-230/lib/systemd/systemd"
hostname=? addr=? terminal=? res=success'
[   72.695713] fbcon: inteldrmfb (fb0) is primary device
[   74.649688] Console: switching to colour frame buffer device 100x80
[   74.660835] i915 0000:00:02.0: fb0: inteldrmfb frame buffer device

The "Memory usable by graphics device" seems to be all RAM available in the
system, 2GiB.

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