Messages in this thread | | | Date | Thu, 30 Mar 2023 18:40:39 +0200 | Subject | Re: [PATCH 18/21] ARM: drop SMP support for ARM11MPCore | From | Neil Armstrong <> |
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Le 30/03/2023 à 12:03, Arnd Bergmann a écrit : > On Thu, Mar 30, 2023, at 09:48, Neil Armstrong wrote: >> On 27/03/2023 14:13, Arnd Bergmann wrote: >>> From: Arnd Bergmann <arnd@arndb.de> >>> >>> The cache management operations for noncoherent DMA on ARMv6 work >>> in two different ways: >>> >>> * When CONFIG_DMA_CACHE_RWFO is set, speculative prefetches on in-flight >>> DMA buffers lead to data corruption when the prefetched data is written >>> back on top of data from the device. >>> >>> * When CONFIG_DMA_CACHE_RWFO is disabled, a cache flush on one CPU >>> is not seen by the other core(s), leading to inconsistent contents >>> accross the system. >>> >>> As a consequence, neither configuration is actually safe to use in a >>> general-purpose kernel that is used on both MPCore systems and ARM1176 >>> with prefetching enabled. >>> >>> We could add further workarounds to make the behavior more dynamic based >>> on the system, but realistically, there are close to zero remaining >>> users on any ARM11MPCore anyway, and nobody seems too interested in it, >>> compared to the more popular ARM1176 used in BMC2835 and AST2500. >>> >>> The Oxnas platform has some minimal support in OpenWRT, but most of the >>> drivers and dts files never made it into the mainline kernel, while the >>> Arm Versatile/Realview platform mainly serves as a reference system but >>> is not necessary to be kept working once all other ARM11MPCore are gone. >> >> Acked-by: Neil Armstrong <neil.armstrong@linaro.org> >> >> It's sad but it's the reality, there's no chance full OXNAS support will >> ever come upstream and no real work has been done for years. >> >> I think OXNAS support can be programmed for removal for next release, >> it would need significant work to rework current support to make it acceptable >> before trying to upstream missing bits anyway. > > Ok, thanks for your reply! > > To clarify, do you think we should plan for removal after the next > stable release (6.3, removed in 6.4), or after the next LTS > release (probably 6.6, removed in 6.7)? As far as I understand, > the next OpenWRT release (23.x) will be based on linux-5.15, > and the one after that (24.x) would likely still use 6.1, unless > they skip an LTS kernel.
I think it's ok to remove it ASAP, or at least before the next LTS, not having SMP makes the platform barely usable so the earliest is the best.
Neil
> > Arnd
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