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Despite being an old ABI, present on all modules, its documentation
is missing. Add it, based on the original commit.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b9c72187abce2b0efd1c41646b1d0c66104d90e4.1632750608.git.mchehab+huawei@kernel.org

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>