On Mon, Apr 08, 2024 at 10:01:32AM -0700, Linus Torvalds wrote: > For our own historical reasons, while we have a few generic atomic > operations: bit operations, cmpxchg, etc, most of our arithmetic and > logical ops all rely on a special "atomic_t" type (later extended with > "atomic_long_t"). > > The reason? The garbage that is legacy Sparc atomics. > > Sparc historically basically didn't have any atomics outside of the > 'test and set byte' one, so if you wanted an atomic counter thing, and > you cared about sparc, you had to play games with "some bits of the > counter are the atomic byte lock". > > And we do not care about that Sparc horror any *more*, but we used to. FWIW, PA-RISC is no better - the same "fetch and replace with constant" kind of primitive as for sparc32, only the constant is (u32)0 instead of (u8)~0. And unlike sparc64, 64bit variant didn't get better.
