Messages in this thread | | | Date | Tue, 28 Mar 2017 16:55:24 +0200 | From | Daniel Lezcano <> | Subject | Re: [PATCH v2 06/18] arm64: arch_timer: Add infrastructure for multiple erratum detection methods |
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On Tue, Mar 28, 2017 at 03:48:23PM +0100, Marc Zyngier wrote: > On 28/03/17 15:36, Daniel Lezcano wrote: > > On Tue, Mar 28, 2017 at 03:07:52PM +0100, Marc Zyngier wrote: > > > > [ ... ] > > > >>>>> -bool arch_timer_check_global_cap_erratum(const struct arch_timer_erratum_workaround *wa, > >>>>> - const void *arg) > >>>>> +bool arch_timer_check_cap_erratum(const struct arch_timer_erratum_workaround *wa, > >>>>> + const void *arg) > >>>>> { > >>>>> - return cpus_have_cap((uintptr_t)wa->id); > >>>>> + return cpus_have_cap((uintptr_t)wa->id) | this_cpu_has_cap((uintptr_t)wa->id); > >>>> > >>>> Not quite. Here, you're making all capability-based errata to be be > >>>> global (if a single CPU in the system has a capability, then by > >>>> transitivity cpus_have_cap returns true). If that's a big-little system, > >>>> you end-up applying the workaround to all CPUs, including those unaffected. > >>>> > >>>> I'd rather drop cpus_have_cap altogether and rely on individual CPU > >>>> matching (since we don't have a need for a global capability erratum > >>>> handling yet). > >>> > >>> Ok, thanks. > >> > >> Quick update. I've just implemented this, and found out that getting rid > >> of local/global has an unfortunate effect: > >> > >> Since we only probe the global errata (using ACPI for example) on the > >> boot CPU path, we lose propagation of the erratum across the secondary > >> CPUs. One way of solving this is to convert the secondary boot path to > >> be aware of DT vs ACPI vs detection method of the month. Which isn't > >> easy, since by the time we boot secondary CPUs, we don't have the > >> pointers to the various ACPI tables anymore. Also, assuming we were > >> careful and saved the pointers, the tables may have been unmapped. Fun. > > > > My proposal was supposed to prevent that. The detecion is done in the > > subsystems, ACPI detects ACPI errata, DT detects DT errata and CPU detects CPU > > errata. The drivers get the errata and enable the workaround. The id > > association <-> errata self contains errata types (void *, char *, int). So > > everything can be done in a CPU basis without local / global dance. > > I'm sorry, but it feels like a Jumbo-Jet sized hammer to try and squash > a fly (I'm staying away from the frozen shark metaphor here). You're > willing to add a whole list of things with private ids that need > matching to kill a flag? I don't think this buys us anything but extra > complexity and another maintenance headache.
Well, it is like your approach except it is split in two steps.
Can you explain where is the extra complexity ? May be I am missing the point.
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