[Bug 74657] Mode detection fails on Dell Venue 8 Pro (due to bad EDID?)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=74657

--- Comment #4 from Adam Williamson <awilliam at redhat.com> ---
>From ajax today:

---

If I'm reading the dmesg there correctly, it looks like that EDID shows up on
the VGA port?  Which could cause problems, since the EDID claims to be for a
digital output, so we might refuse to believe it's attached to an analog port. 
But also:

eb 06 20:04:30 localhost kernel: [drm:valleyview_crt_detect_hotplug],
valleyview hotplug adpa=0xf40000, result 0
Feb 06 20:04:30 localhost kernel: [drm:intel_crt_detect], CRT detected via
hotplug
Feb 06 20:04:30 localhost kernel: [drm] GMBUS [i915 gmbus vga] timed out,
falling back to bit banging on pin 2
Feb 06 20:04:30 localhost kernel: [drm:drm_do_probe_ddc_edid], drm: skipping
non-existent adapter i915 gmbus vga
Feb 06 20:04:30 localhost kernel:
[drm:drm_helper_probe_single_connector_modes], [CONNECTOR:9:VGA-1] probed modes
:
Feb 06 20:04:30 localhost kernel: [drm:drm_mode_debug_printmodeline], Modeline
21:"1024x768" 60 65000 1024 1048 1184 1344 768 771 777 806 0x40 0xa
Feb 06 20:04:30 localhost kernel: [drm:drm_mode_debug_printmodeline], Modeline
19:"800x600" 60 40000 800 840 968 1056 600 601 605 628 0x40 0x5
Feb 06 20:04:30 localhost kernel: [drm:drm_mode_debug_printmodeline], Modeline
18:"800x600" 56 36000 800 824 896 1024 600 601 603 625 0x40 0x5
Feb 06 20:04:30 localhost kernel: [drm:drm_mode_debug_printmodeline], Modeline
20:"848x480" 60 33750 848 864 976 1088 480 486 494 517 0x40 0x5
Feb 06 20:04:30 localhost kernel: [drm:drm_mode_debug_printmodeline], Modeline
17:"640x480" 60 25175 640 656 752 800 480 489 492 525 0x40 0xa

It looks like Linux is failing to read DDC off the VGA port (possibly not
surprising, the EDID might be in the VBT instead of on the other end of I2C). 
But we're only going to look in the VBT for EDID for LVDS or eDP, and since
this appears to be VGA not LVDS...

Anyway that could be the bug, it could also not.  If it's not that then I'd
want to manually step through i915 init to figure it out.

---

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