[why] dc_stream_state containing a pointer to sink is poor design. Sink describes the display, and the specifications or capabilities it has. That information is irrelevant for dc_stream_state, which describes hardware state, and is generally used for hardware programming. It could further be argued that dc_sink itself is just a convenience dc provides, and DC should be perfectly capable of programming hardware without any dc_sinks (for example, emulated sinks). [how] Phase 1: Deprecate use of dc_sink pointer in dc_stream. Most references are trivial to remove, but some call sites are risky (such as is_timing_changed) with no obvious logical replacement. These will be removed in follow up change. Add dc_link pointer to dc_stream. This is the typical reason DC really needed sink pointer, and most call sites are replaced with this. DMs also need minor updates, as all 3 DMs leverage stream->sink for some functionality. this is replaced instead by a pointer to private data inside dc_stream_state, which is used by DMs as a quality of life improvment for some key functionality. it allows DMs to set pointers have to their own objects which associate OS objects to dc_stream_states (such as DisplayTarget and amdgpu_dm_connector). Without the private pointer, DMs would be forced to perform a lookup for callbacks. Signed-off-by: Jun Lei <Jun.Lei@amd.com> Reviewed-by: Aric Cyr <Aric.Cyr@amd.com> Acked-by: David Francis <David.Francis@amd.com> Acked-by: Leo Li <sunpeng.li@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>