Messages in this thread | | | Date | Thu, 18 Jan 2018 14:21:26 +0000 | From | Dave Martin <> | Subject | Re: [PATCH v2 0/2] arm64: Run enable method for errata work arounds on late CPUs |
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On Thu, Jan 18, 2018 at 12:08:43PM +0000, Robin Murphy wrote: > On 18/01/18 12:00, Robin Murphy wrote: > [...] > >>+struct enable_arg { > >>+ int (*enable)(struct arm64_cpu_capabilities const *); > >>+ struct arm64_cpu_capabilities const *cap; > >>+}; > >>+ > >>+static int __enable_cpu_capability(void *arg) > >>+{ > >>+ struct enable_arg const *e = arg; > >>+ > >>+ return e->enable(e->cap); > >>+} > > > >AFAICS, you shouldn't even need the intermediate struct - if you were > >instead to call stop_machine(&caps->enable, ...), the wrapper could be: > > > > <type> **fn = arg; > > *fn(container_of(fn, struct arm64_cpu_capabilities, enable)); > > > >(cheaty pseudocode because there's no way I'm going to write a > >pointer-to-function-pointer type correctly in an email client...) > > > >That's certainly a fair bit simpler in terms of diffstat; whether it's > >really as intuitive as I think it is is perhaps another matter, though. > > Ah, right, but then you'd be back to casting away const, and at that point > it makes no sense to do the container_of dance instead of just passing the > struct pointer itself around... > > I shall now excuse myself from this discussion, as I'm clearly not helping > :) > > Robin.
That's what I was about to say... but neat trick.
However, it does concentrate the type fudge in one place and keeps the arm64_cpu_capabilities::enable() prototype correct, so it's still better than the original.
Thinking about it, the following is probably clearer and no worse:
static int __enable_cpu_capability(void *arg) { struct arm64_cpu_capabilities const *cap = arg;
return cap->enable(cap); }
...
stop_machine(__enable_cpu_capability, (void *)caps, cpu_online_mask);
In your version, the argument would be (void *)&caps->enable, which is really just a proxy for (void *)caps, unless I missed something.
What do you think Suzuki? I can respin my patch if you fancy picking it up. Either way, it's not urgent.
Cheers ---Dave
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