Re: [PATCH v2 cmpxchg 12/13] sh: Emulate one-byte cmpxchg

Arnd Bergmann
2024-05-02T21:50:44Z

On Thu, May 2, 2024, at 15:33, Paul E. McKenney wrote:
> On Thu, May 02, 2024 at 07:11:52AM +0200, John Paul Adrian Glaubitz wrote:
>> On Wed, 2024-05-01 at 22:06 -0700, Paul E. McKenney wrote:
>> > > Does cmpxchg_emu_u8() have any advantages over the native xchg_u8()?
>> >
>> > That would be 8-bit xchg() rather than 8-byte cmpxchg(), correct?
>>
>> Indeed. I realized this after sending my reply.
>
> So this one-byte-only series affects only Alpha systems lacking
> single-byte load/store instructions. If I understand correctly, Alpha
> 21164A (EV56) and later *do* have single-byte load/store instructions,
> and thus are still just fine. In fact, it looks like EV56 also has
> two-byte load/store instructions, and so would have been OK with
> the original one-/two-byte RFC series.

Correct, the only other architecture I'm aware of that is missing
16-bit load/store entirely is ARMv3.

> Arnd will not be shy about correcting me if I am wrong. ;-)

I'll take this as a reminder to send out my EV4/EV5 removal
series. I've merged my patches with Al's bugfixes and rebased
all on top of 6.9-rc now. It's a bit late now, so I'll
send this tomorrow:

https://git.kernel.org/pub/scm/linux/kernel/garch/alpha/include/asm/cmpxchg.hit/arnd/asm-generic.git/log/?h=alpha-cleanup-6.9

Arnd