[Intel-gfx] [PATCH 6/8] drm/i915/dp: clear DP encoder CRTC if the receiver disappears

[Keith Packard]

On Fri, 1 Jul 2011 16:59:48 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:

> That depends on what behavior we want.  With the previous fixes, if you
> unplug, we'll get a hotplug event, fail to detect a link, and tear down
> the receiver.  With the old code you'd get bad behavior unless you had
> hit a DPMS path earlier.

Yeah, the old code was clearly wrong; this looks like something that
needs fixing, I just don't know what the right fix is.

> A subsequent hotplug will be ignored as far as link training goes, since
> we don't have a receiver configured.

Do we need separate variables for 'should be configured' and 'actually is
configured' then? We need to know if there is a configuration we should
be selecting, and then we need to know whether the display is actually
using that configuration.

> In both cases, we'll emit hotplug events to userspace, which is free to
> react (or not) however it wants.

Let's assume (for now) that user space doesn't do anything. That seems
like a good first step to get right; we should assume that if user space
sets some mode then it should work correctly.

> So I think we'd need to leave the receiver_configured bit set even if
> the hot plug re-train failed, and just try it again on the next hot
> plug (assuming we want to preserve user configs across hot plug
> events and not just let userspace handle the hotplug events).

I don't think we want to lose the user config -- in the absence of any
user-driven changes, we want to reset the mode exactly as it was when
the monitor is plugged back in.

-- 
keith.packard at intel.com
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