在2024年6月21日六月 下午2:57，Maciej W. Rozycki写道： > On Fri, 21 Jun 2024, Jiaxun Yang wrote: > >> > I think this ought not to be done in two places independently and the >> > pieces in <asm/mach-*/cpu-feature-overrides.h> need to be removed, likely >> > in the same change even, *however* not without double-checking whether >> > there is not a case among them where a platform actually has LL/SC support >> > disabled despite the CPU used there having architectural support for the >> > feature. Otherwise we may end up with a case where a platform has LL/SC >> > support disabled via its <asm/mach-*/cpu-feature-overrides.h> setting and >> > yet we enable ARCH_SUPPORTS_ATOMIC_RMW or ARCH_HAVE_NMI_SAFE_CMPXCHG for >> > it via Kconfig. >> >> IMO it's necessary for platforms who know what are they doing such as ATH25, >> which we took care in this series. >> >> I'll add a build time assertion to ensure when CONFIG_CPU_HAS_LLSC is selected >> kernel_uses_llsc is statically 1, so any incorrect overrides can be spotted >> at build time. > > That might do in the interim as a sanity check, however ultimately the > sole reason these <asm/mach-*/cpu-feature-overrides.h> exist (and the > `cpu_has_llsc' setting there) is so that a dynamic check at run time is > avoided where the result is known from elsewhere beforehand anyway, and > your change effectively supersedes the overrides, and therefore they need > to be removed. > No, overrides are still valid if platform did CPU_MAY_HAVE_LLSC, this is at least valid for R10000 systems (IP28 decided to opt-out from llsc somehow), ATH25 (platform made assumption on IP version shipped with CPU), cavium octeon (platform decided to opt-out llsc for non-SMP build). I'm not confident with handling them all in Kconfig so I think the best approach so far is to do build time assertion. Does anyone reckon the reason behind opt-out LLSC for IP28? As far as I understand there is no restriction on using LLSC after workaround being applied. If it's purely performance reason, I think I'll need to move kernel_uses_llsc logic to Kconfig as well. Thanks > > Maciej -- - Jiaxun
