drm/fb-helper: Try to protect cleanup against delayed setup

Some vague evidences suggests this can go wrong. Try to prevent it by
holding the right mutex and clearing ->deferred_setup to make sure we
later on don't accidentally try to re-register the fbdev when the
driver thought it had it all cleaned up already.

v2: I realized that this is fundamentally butchered, and CI complained
about lockdep splats. So limit the critical section again and just add
a few notes what the proper fix is.

References: https://intel-gfx-ci.01.org/tree/linux-next/next-20201215/fi-byt-j1900/igt@i915_pm_rpm@module-reload.html
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>

0 files changed, 0 insertions, 0 deletions