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SubjectRe: [PATCH 08/16] arm64: capabilities: Group handling of features and errata
On Fri, Jan 26, 2018 at 12:31:18PM +0000, Suzuki K Poulose wrote:
> On 26/01/18 11:47, Dave Martin wrote:
> >On Tue, Jan 23, 2018 at 12:28:01PM +0000, Suzuki K Poulose wrote:
> >>So far we have had separate routes for triggering errata and feature
> >
> >"triggering errata" ? ;)
> >
>
> :-). Should have been "triggering errata and feature capability *checks*.
>
> >Maybe "[...] for determining whether to activate errata workarounds and
> >whether to enable feature capabilities."
> >
>
>
> >>capabilities. Also, we never allowed "features" based on local CPU
> >>and "errata" based on System wide safe registers. This patch
> >>groups the handling of errata and features and also allows them
> >>to have all the possible scopes.
> >>
> >>So, we now run through the arm64_features and arm64_errata:
> >
> >when?
>
> with this patch.

I mean, when at runtime?

> >What about late cpus?
> >
>
> We don't detect any new capabilities on them. They continue to get
> verified against the enabled capabilities.
>
> >> 1) with SCOPE_LOCAL_CPU filter on each boot time enabeld CPUs,
> >> via update_cpu_local_capabilities().
> >
> >"each [...] enabeld CPUs" -> "each [...] enabled CPU"
> >
> >Also, changing "boot time" -> "boot-time" helps avoid this being misread
> >as "on each boot", which could be taken to mean "each time a CPU comes
> >online". I'm guessing that's not the intended meaning here.
>
> OK

[...]

> >[Gaah, stupid git diff making function insertion look like function
> >modification. Sometimes --patience does a better job, but there seems
> >no foolproof solution... If you do a respin, it might be worth trying
> >it.]
>
> Will try, thanks for the suggestion. I didn't know about that :-)

YMMV though. The output is different, but it's not always better...

> >>-static void __init setup_feature_capabilities(void)
> >>+static void __init setup_system_capabilities(void)
> >> {
> >>- update_cpu_capabilities(arm64_features,
> >>- ARM64_CPUCAP_TYPE_ALL, "detected feature:");
> >>- enable_cpu_capabilities(arm64_features, ARM64_CPUCAP_TYPE_ALL);
> >>+ /*
> >>+ * We have finalised the system wide safe feature registers,
> >>+ * finalise the capabilities that depend on it.
> >>+ */
> >>+ update_system_capabilities();
> >>+ /* Enable all the available capabilities */
> >>+ enable_cpu_capabilities(ARM64_CPUCAP_TYPE_ALL);
> >
> >So setup_system_capabilities() enables _non_ system-wide capabilities/
> >errata workarounds too?
>
> >Maybe this function should just have a different name, like
> >"setup_boot_capabilities" or similar?
>
> The problem with setup_boot_capabilities() is that it could conflict with
> "coming soon" setup_boot_cpu_capabilities(). May be,
>
> setup_boot_time_system_capabilities().

Maybe. If no name leaps out as better, maybe it's not worth changing
it.

> >
> > }
> >> DEFINE_STATIC_KEY_FALSE(arm64_const_caps_ready);
> >>@@ -1422,9 +1435,7 @@ void __init setup_cpu_features(void)
> >> u32 cwg;
> >> int cls;
> >>- /* Set the CPU feature capabilies */
> >>- setup_feature_capabilities();
> >>- enable_errata_workarounds();
> >>+ setup_system_capabilities();
> >> mark_const_caps_ready();
> >> setup_elf_hwcaps(arm64_elf_hwcaps);
> >
> >I wonder whether we could unify the elf hwcaps handling too.
>
> I was thinking about it today. The only catch is how do we know
> if we have "the capability", as it is spread across multiple bitmasks.
> (HWCAP, COMPAT_HWCAP, COMPAT_HWCAP2).

An easy-ish solution might be to maintain our own bitmap in the style
of cpu_hwcaps, and set bits in parallel with the elf_hwcap etc. bits.
Or, add a method that knows how to set/query the appropriate bit.

I guess we could do this later. It's certainly not urgent.

Cheers
---Dave

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