[Bug 85924] [hsw DP-to-DVI] DP hot plug fails if booted without Monitor Attached

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85924

--- Comment #48 from Todd Previte <tprevite at gmail.com> ---
Created attachment 115935
  --> https://bugs.freedesktop.org/attachment.cgi?id=115935&action=edit
Fix for passive DP->DVI/HDMI dongles

In light of Jean's comments, I looked further into this bug. This problem is
related to the fix for bug #41059 - the code put in place there stops of the
execution of that internal loop which makes a second attempt to probe the DDC.
And that's where things go wrong for the DP dongles.

This patch supersedes the previous work-around patch I posted. This is a
cleaner solution that doesn't require the usleep_range() delays that the higher
level function patch did. This patch also preserves (as much as possible) the
spirit and intent of the solution for #41059, in that the code shouldn't
repeatedly flog a non-existent or unresponsive adapter, thus delaying things
unnecessarily. With this patch, a single NAK will be tolerated and the loop
will continue. A second NAK happens and it will break out of the loop as it did
previously.

If you have these passive DP->DVI/HDMI adapters, please test with this patch
applied.


-T

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