On Tue, Dec 15, 2020 at 12:26:10PM +0100, Arnd Bergmann wrote: > On Tue, Dec 15, 2020 at 7:09 AM Guo Ren <guoren@xxxxxxxxxx> wrote: > > On Mon, Dec 14, 2020 at 9:15 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: > > > I had a look at what other architectures always implement > > > futex_atomic_cmpxchg_inatomic() or can use the asm-generic non-SMP version, > > > and I found that it's pretty much all of them, the odd ones being just sparc32 > > > and csky, which use asm-generic/futex.h but do have an SMP option, > > > as well as xtensa > > > > > > I would guess that for csky, this is a mistake, as the architecture is fairly > > > new and should be able to implement it. Not sure about sparc32. > > > > The c610, c807, c810 don't support SMP, so futex_cmpxchg_enabled = 1 > > with asm-generic's implementation. > > For c860, there is no HAVE_FUTEX_CMPXCHG and cmpxchg_inatomic/inuser > > implementation, so futex_cmpxchg_enabled = 0. > > > > Thx for point it out, we'll implement cmpxchg_inatomic/inuser for C860 > > and still use asm-generic for non-smp CPUs. > > Sounds good to me. > > With that, I would suggest we actually remove the -ENOSYS fallback > for arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic() > in asm-generic/futex.h as well as the HAVE_FUTEX_CMPXCHG Kconfig > symbol, plus these additional fixups: > > - for xtensa and mips configurations without ll/sc, fall back to the > asm-generic version. These are all uniprocessor, while the > corresponding SMP machines have a working > arch_futex_atomic_op_inuser(). > > - Disable SMP support for sun4m/sun4d. From the historic git > tree, it's unclear how well this ever worked, and very few machines > of this class ever existed Hooray!! what about PA-RISC ? Can we burn that too?
