drm/kms: Duct-tape for mode object lifetime checks

drm/kms: Duct-tape for mode object lifetime checks

commit 7bf14b3bbff53c95da2a69bfac14fa4bde9aefba
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Jun 14 08:17:23 2019 +0200

    drm/kms: Catch mode_object lifetime errors

uncovered a bit a mess in dp drivers. Most drivers (from a quick look,
all except i915) register all the dp stuff in their init code, which
is too early. With CONFIG_DRM_DP_AUX_CHARDEV this will blow up,
because drm_dp_aux_register tries to add a child to a device in sysfs
(the connector) which doesn't even exist yet.

No one seems to have cared thus far. But with the above change I also
moved the setting of dev->registered after the ->load callback, in an
attempt to keep old drivers from hitting any WARN_ON backtraces. But
that moved radeon.ko from the "working, by accident" to "now also
broken" category.

Since this is a huge mess I figured a revert would be simplest. But
this check has already caught issues in i915:

commit 8b440256b8814cb014d441de561840f9f559b7f7
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Tue Aug 20 19:16:57 2019 +0300

    drm/i915: Do not create a new max_bpc prop for MST connectors

Hence I'd like to retain it. Fix the radeon regression by moving the
setting of dev->registered back to were it was, and stop the
backtraces with an explicit check for dev->driver->load.

Everyone else will stay as broken with CONFIG_DRM_DP_AUX_CHARDEV. The
next patch will improve the kerneldoc and add a todo entry for this.

Fixes: 7bf14b3bbff5 ("drm/kms: Catch mode_object lifetime errors")
Cc: Sean Paul <sean@poorly.run>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reported-by: Michel Dänzer <michel@daenzer.net>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Tested-by: Michel Dänzer <mdaenzer@redhat.com>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190917120936.7501-1-daniel.vetter@ffwll.ch