Messages in this thread | | | From | Huacai Chen <> | Date | Thu, 11 Aug 2022 16:44:08 +0800 | Subject | Re: [PATCH] LoongArch: Fix the !CONFIG_SMP build for irqchip drivers |
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Hi, Marc and Xuerui,
On Thu, Aug 11, 2022 at 2:56 PM Marc Zyngier <maz@kernel.org> wrote: > > On Thu, 11 Aug 2022 01:58:15 +0100, > WANG Xuerui <kernel@xen0n.name> wrote: > > > > On 8/10/22 23:38, Huacai Chen wrote: > > > > > Hi, Marc, > > > > > > On Wed, Aug 10, 2022 at 7:01 PM Marc Zyngier <maz@kernel.org> wrote: > > >> On 2022-08-10 11:31, Huacai Chen wrote: > > >>> 1, Guard get_ipi_irq() in CONFIG_SMP; > > >>> 2, Define cpu_logical_map() for the EIOINTC driver; > > >>> 3, Make eiointc_set_irq_affinity() return early for !CONFIG_SMP. > > >>> > > >>> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> > > >> Frankly, the real question is why do you even bother? As far as > > >> I can tell, LoongArch has no UP system. > > >> > > >> arm64 crossed that bridge a long time ago, and we never looked > > >> back, because these systems hardly exist. > > >> > > >> I'd rather you simply have a CONFIG_SMP always set to 'y', and > > >> be done with it forever. > > > LoongArch also has low-end processors (even LoongArch64). Though we > > > haven't translate all documents at > > > https://loongson.github.io/LoongArch-Documentation/ in time, there are > > > currently 4 LoongArch64 processors: Loongson-2K500 (single-core), > > > Loongon-2K1000 (dual-core), Loongson-3A5000 (quad-core) and > > > Loongson-3C5000 (16-core). So we indeed need a UP configuration. > > > Thanks. > > > > I remember seeing an alternatives mechanism in the works for > > LoongArch. If such alternatives mechanism is to be upstreamed in short > > order, why make SMP one more build-time time option that developers > > have to decide upon? It's not like SMP code would break, or run with > > unacceptable overhead, on UP systems AFAIK, so it's probably better to > > not preemptively support so many *possibilities* that haven't been > > realized so the *current* maintainability suffers. Practically one > > can't buy the LoongArch 2K line of products anywhere right now, and > > the few companies developing for it are likely not using upstream > > kernels anyway, so it's not like we can't wait either. > > And that's exactly my point. Yes, it is always possible to build a UP > system. But is it worth *maintaining* a configuration option for this? > I seriously doubt it. > > My advise is to stick to SMP only for now (it will run just fine on a > UP machine), and only if upstream users find it completely > unacceptable should a !SMP option be introduced, or make it a runtime > decision (32bit ARM has had SMP_ON_UP support for a long time). OK, I will drop this patch and follow the ARM64 method, thanks.
Huacai > > M. > > -- > Without deviation from the norm, progress is not possible.
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