On Wed, Dec 10, 2014 at 04:48:18PM +0100, Andrzej Hajda wrote:

3. There are drivers which can work without specific resource, but if
  the resource becomes available/unavailable it can do some additional stuff.
  An example of such driver is DRM driver (more precisely drm_connector) -
  it can start without attached drm_panel, but if the panel becomes available it
  can react by generating HPD event and start using it.

Bad example, and actually incorrect.  DRM connectors are referenced in
userspace by an IDR number, which can be re-used in the case of a
connector appearing, disappearing, and then a different connector
re-appearing.

DRM really is *not* safe to hotplug like this: DRM is more a card-level
thing, which is why we have the component helpers - which allow us to
merge several devices into one logical card-like device in a generic
manner.

DRM needs a stable picture of the CRTCs, encoders and connectors, which
should _never_ change during the lifetime of the DRM device.  Devices
attached to connectors can be hotplugged, but that's about the limit of
hot-plugging in DRM.

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