This is a lot of prep-work for being able to send event notifications
back to userspace. Events now contain data, rather than a "something
just happened" signal.
Handler data is now embedded into a containing structure, rather than
being kmalloc()'d, and can optionally have the notify routine handled
in a workqueue.
Various races between suspend/unload with display HPD/DP IRQ handlers
automagically solved as a result.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
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