locking/Documentation: State purpose of memory-barriers.txt

To repeat, this document is not a specification of what Linux expects from

To repeat, this document is not a specification of what Linux expects from

hardware.

hardware.

The purpose of this document is twofold:

 (1) to specify the minimum functionality that one can rely on for any

     particular barrier, and

 (2) to provide a guide as to how to use the barriers that are available.

Note that an architecture can provide more than the minimum requirement

for any particular barrier, but if the architecure provides less than

that, that architecture is incorrect.

Note also that it is possible that a barrier may be a no-op for an

architecture because the way that arch works renders an explicit barrier

unnecessary in that case.

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CONTENTS

CONTENTS

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