I tried to put some real-time related documentation.   
Patch #1 SPDX tag to seqlock.
Patch #2 extends locktypes with local_lock_nested_bh
Patch #3 adds some real-time bits.

In case there is something missing or unclear, please let me know.

v1…v2:
  - #1 does not add a reference tag anymore.
  - #2 wording/ typo in #2
  - #3 is moved to core-api
  - #3 does not uses rst references but uses the plain file name
  - #3 is extended with some notes for architecture porting.

Sebastian Andrzej Siewior (3):
  Documentation: seqlock: Add a SPDX license identifier
  Documentation: locking: Add local_lock_nested_bh() to locktypes
  Documentation: Add real-time to core-api

 Documentation/core-api/index.rst              |   1 +
 .../real-time/architecture-porting.rst        | 109 ++++++++
 .../core-api/real-time/differences.rst        | 242 ++++++++++++++++++
 Documentation/core-api/real-time/index.rst    |  16 ++
 Documentation/core-api/real-time/theory.rst   | 116 +++++++++
 Documentation/locking/locktypes.rst           |  21 ++
 Documentation/locking/seqlock.rst             |   2 +
 7 files changed, 507 insertions(+)
 create mode 100644 Documentation/core-api/real-time/architecture-porting.rst
 create mode 100644 Documentation/core-api/real-time/differences.rst
 create mode 100644 Documentation/core-api/real-time/index.rst
 create mode 100644 Documentation/core-api/real-time/theory.rst

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2.50.1