linux-kernel - Re: [PATCH] arm64: cpufeature: Display the set of cores with a feature

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Message-ID: <20231013082948.GA13431@willie-the-truck>
Date:   Fri, 13 Oct 2023 09:29:48 +0100
From:   Will Deacon <will@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        mark.rutland@....com, maz@...nel.org, anshuman.khandual@....com,
        krisman@...e.de, broonie@...nel.org, james.morse@....com,
        ionela.voinescu@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: cpufeature: Display the set of cores with a
 feature

On Thu, Oct 12, 2023 at 08:30:16PM -0500, Jeremy Linton wrote:
> The AMU feature can be enabled on a subset of the cores in a system.
> Because of that, it prints a message for each core as it is detected.
> This becomes tedious when there are hundreds of cores. Instead, for
> CPU features which can be enabled on a subset of the present cores,
> lets wait until update_cpu_capabilities() and print the subset of cores
> the feature was enabled on.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>  arch/arm64/include/asm/cpufeature.h |  2 ++
>  arch/arm64/kernel/cpufeature.c      | 16 +++++++++++++---
>  2 files changed, 15 insertions(+), 3 deletions(-)

That's pretty neat. Are there any other caps we could switch over to this
new mechanism as well? We have a weird bodge, for example, in has_hw_dbm()
to print a "detected: ..." message and I wonder whether following the
example of the AMU would be better?

Will