On 29/01/18 17:14, Dave Martin wrote:

On Fri, Jan 26, 2018 at 12:31:18PM +0000, Suzuki K Poulose wrote:

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On 26/01/18 11:47, Dave Martin wrote:

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On Tue, Jan 23, 2018 at 12:28:01PM +0000, Suzuki K Poulose wrote:

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So far we have had separate routes for triggering errata and feature

"triggering errata" ? ;)

:-). Should have been "triggering errata and feature capability *checks*.

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Maybe "[...] for determining whether to activate errata workarounds and
whether to enable feature capabilities."

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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?

Sorry, I thought that was evident from the comment below :

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What about late cpus?

We don't detect any new capabilities on them. They continue to get
verified against the enabled capabilities.

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  1) with SCOPE_LOCAL_CPU filter on each boot time enabeld CPUs,
     via update_cpu_local_capabilities().

Here ^^.  Earlier we ran only through the errata list. But now, we
run through errata and the features, using a type filter of SCOPE_LOCAL_CPU.

It also said :

   2) with SCOPE_SYSTEM filter only once after all boot time enabled
     CPUs are active.

(2) happens from setup_cpu_features(), just like it was done earlier, but
with a filter of SCOPE_SYSTEM.

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"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.

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   }

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  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.

Yes, I understand.

Cheers
Suzuki