On Mon, Apr 04, 2016 at 07:41:40AM +0100, Paul Burton wrote: > > On 01/04/2016 13:48, Paul Burton wrote: > > >On Thu, Mar 17, 2016 at 09:08:09PM +0000, Qais Yousef wrote: > > >>Malta defconfig compiles with GIC on. Hence when compiling for SMP it causes the > > >>new IPI code to be activated. But on qemu malta there's no GIC causing a > > >>BUG_ON(!ipidomain) to be hit in mips_smp_ipi_init(). > > >> > > >>Since in that configuration one can only run a single core SMP (!), skip IPI > > >>initialisation if we detect that this is the case. It is a sensible behaviour > > >>to introduce and should keep such possible configuration to run rather than die > > >>hard unnecessarily. > > >Hi Qais/Ralf, > > > > > >This patch is insufficient I'm afraid. It's entirely possible to use SMP > > >with multiple VPEs in a single core on Malta boards that don't have a > > >GIC - we have code handling IPIs in that case guarded by #ifdef > > >CONFIG_MIPS_MT_SMP in arch/mips/mti-malta/malta-int.c. I think the > > >BUG_ON needs to be removed entirely, unless that single-core multi-VPE > > >IPI code is also converted to use an IPI irqdomain. > > > > > > > I was under the impression that SMP is only supported under GIC and older > > forms of SMP are deprecated. > > Hi Qais, > > That's incorrect. We're talking about systems that don't have any GIC - > there are Malta configurations that don't. QEMU is the obvious one, and > you can break it (at least v2.5.0 which has no GIC) with this patch just > by using "-cpu 34Kf -smp 2" to show up 2 VPEs. I believe there are also > real bitfiles (though probably unused these days) that would have the > same problem. > > > I think the problem you're describing is different to the one this is trying > > to fix. The right fix for your issue is to make CONFIG_GENERIC_IRQ_IPI > > selected when CONFIG_MIPS_GIC && !CONFIG_MIPS_MT_SMP. > > > > Would it be easy for you to create such a patch and test it? > > That would be insufficient, since we can have a kernel that includes GIC > support & CONFIG_MIPS_MT_SMP (SMVP) support and not know whether > there'll actually be a GIC or multiple VPEs until runtime. So Kconfig > cannot solve this at compile time. > > I believe that the best thing to do would be to convert the single-core > MT IPI code to use the IRQ domain stuff you added (which I don't see any > documentation for & am currently struggling to decipher). But given that > we're post-merge-window on the way to v4.6 I think the best we can do is > to just return when there's no IPI domain, rather than BUG_ON. I'll > submit a patch to do that later this morning. FYI, Qais' initial fix is in the pull request I sent to Linus yesterday so any fixes please relative to that patch. Ralf
