drm/i915 does not detect LVDS modes

Hello

When loading i915 with macboopro6,2 (with debug on) the following shows:

---
[drm:pid1201:do_gmbus_xfer] GMBUS [i915 gmbus panel] NAK for addr: 0050 w(1)
[drm:pid1201:do_gmbus_xfer] GMBUS [i915 gmbus panel] NAK on first message,
retry
[drm:pid1201:do_gmbus_xfer] GMBUS [i915 gmbus panel] NAK for addr: 0050 w(1)
[drm:pid1201:drm_do_probe_ddc_edid] drm: skipping non-existent adapter i915
gmbus panel
[drm:pid1201:intel_lvds_init] No LVDS modes found, disabling.
---

and the result is a frozen screen. The keyboard works and I can ssh to the
machine to reboot.

However, linux-4.9 gives

---
[drm:gmbus_xfer [i915]] GMBUS [i915 gmbus panel] timed out after NAK
[    5.668588] [drm:gmbus_xfer [i915]] GMBUS [i915 gmbus panel] NAK for
addr: 0050 w(1)
[    5.683016] [drm:intel_lvds_init [i915]] using preferred mode from EDID:
[    5.683070] [drm:drm_mode_debug_printmodeline [drm]] Modeline
35:"1680x1050" 60 119000 1680 1728 1760 1840 1050 1053 1059 1080 0x48 0xa
---

and the screen/keyboard work fine.

I am focusing on intel_lvds.c to bring it closer to drm/i915 linux-4.9;
however, maybe I am missing something obvious---can anyone give suggestions
as to where else to look?

Cheers

Peeter

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