drm/i915/guc: Introduce context parent-child relationship
Introduce context parent-child relationship. Once this relationship is
created all pinning / unpinning operations are directed to the parent
context. The parent context is responsible for pinning all of its
children and itself.
This is a precursor to the full GuC multi-lrc implementation but aligns
to how GuC mutli-lrc interface is defined - a single H2G is used
register / deregister all of the contexts simultaneously.
Subsequent patches in the series will implement the pinning / unpinning
operations for parent / child contexts.
v2:
(Daniel Vetter)
- Add kernel doc, add wrapper to access parent to ensure safety
v3:
(John Harrison)
- Fix comment explaing GEM_BUG_ON in to_parent()
- Make variable names generic (non-GuC specific)
v4:
(John Harrison)
- s/its'/its/g
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014172005.27155-8-matthew.brost@intel.com