[Intel-gfx] intel_dp_detect redesign

[Daniel Vetter]

Hi Ander&Sivakumar,

Dave&I had a short discussion about reprobing DP (and MST) state on
resume. I think this is something we've missed in our dp hpd handling
rework thus far. And at least for SST we need to take it into account
since it would be a regression.

Currently it's done through ->detect callback from
drm_helper_hpd_irq_event called from i915_drm_resume. Also irc logs
below.

Thanks, Daniel

<airlied> danvet: so probing on resume, it seems a bit inconsistent,
is the kernel driver meant to be doing it?
<airlied> I think since we stopped vt switching we've stopped doing
it, which is making mst docking kinda suck
<danvet> mst was after stopping vt-switching I thought
<danvet> but yeah we should reprobe
<danvet> and we do (at least occasionally if it's not broken again)
<airlied> well people are just noticing it more with mst
<danvet> but not for mst iirc
<danvet> mst just restores and hopes I think
<airlied> but when you suspend in the dock, and move the laptop, and
resume things don't work unless you xrandr
<airlied> and vice-versa
<danvet> I looked into it for 5 minutes when tedtso complained an ran ;-)
<airlied> well reproving should bring up/tear down any mst
<danvet> hm, xrandr shouldn't be enough to fix it, we need a real hpd
to redo the mst stuff I thought ...
<airlied> so I don't think mst is special here
<danvet> we reprobe through probe helpers
<robclark> janesma, Pali, bleh sorry.. yeah, looks like it needs a
stdbool.h.. not sure why I didn't hit that compile error.. sorry about
that..
<danvet> all mst stuff is done directly from hpd since it needs to
know long vs. short
<danvet> so it misses out
<airlied> if we probe a DP port and the device is gone, MST will get torn down
<airlied> danvet: not so
<airlied> unless someone else has been hacking the driver
* xxmitsu (~mike at 5-15-26-95.residential.rdsnet.ro) has joined #dri-devel
<danvet> oh, the completely gone case
* danvet looks
<airlied> oh maybe we don't handle that properly
<airlied> oh you might be right, I wonder where we should hook that in
<danvet> drm_helper_hpd_irq_event in i915_drm_resume should get this
right for non-mst
<danvet> well non-DP maybe, anderco and rtshiva are reworking this
<danvet> but it's not merged yet
<airlied> I'm guessing detect should not if a port was in mst
<airlied> and is now disconnected
<danvet> ok, skeleton is there but not all
<airlied> intel_dp_detect
<danvet> drm_dp_mst_topology_mgr_resume should probably check the
entire hierarchy, not just a simple dpcd write
<danvet> and if anything changes, we need to generate the uevent somewhere
<danvet> so might be better to re-run the entire dp_detect pile
<danvet> tricky part is that we need to lie about long vs. short
<danvet> it should be treated like a long hpd if anything changed,
short otherwise
<danvet> well we have mgr->cbs->hotplug in the mst manager already
<danvet> so should reuse that hook
<danvet> airlied, I guess just fix up drm_dp_mst_topology_mgr_resume
to do rescan the entire hierarchy
<danvet> calling ->hotplug if anything changed
<danvet> and only returning true if the sink isn't mst any more
<danvet> along the lines of what intel_dp_probe_mst does
<danvet> it's not going to be all that simple ;-)
<danvet> at least if you care about stuff like laptopt connected to
dock -> screen
<danvet> s/r
<airlied> doesn't sounds like fun, I'll stick on my list of things to
be scared off
<danvet> then laptop only connected to dock
<danvet> airlied, done the same
<airlied> well the use case is laptop in dock, suspend, resume with
laptop plugged into a monitor
<danvet> but the fun part is that anderco/rtshiva want to rework this
<danvet> and if they do they'll also break sst dp ;-)
<danvet> so I think I have some victims
<danvet> airlied, yeah that's step one
<airlied> I'd prefer to get the fixes in before redesigning the tower
<danvet> but that already has all the complexity on the driver side
<danvet> only thing missing is the code in the mst helper to rescan
the entire tree and call ->hot_plug if needed
<danvet> problem is that current dp hpd handling is a mess already
<danvet> it's hard to fix anything in there atm
<danvet> so fixing this properly is needed anyway
<danvet> it's just that I've forgotten about the resume case for plain
DP myself ;-)

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch