linux-kernel - Re: [PATCH] arm64: Run enable method for errata work arounds on late CPUs

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Message-ID: <20180117143816.GF22781@e103592.cambridge.arm.com>
Date:   Wed, 17 Jan 2018 14:38:16 +0000
From:   Dave Martin <Dave.Martin@....com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        Andre Przywara <andre.przywara@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: Run enable method for errata work arounds on late
 CPUs

On Wed, Jan 17, 2018 at 01:22:19PM +0000, Suzuki K Poulose wrote:
> On 17/01/18 12:25, Dave Martin wrote:
> >On Wed, Jan 17, 2018 at 10:05:56AM +0000, Suzuki K Poulose wrote:
> >>When a CPU is brought up after we have finalised the system
> >>wide capabilities (i.e, features and errata), we make sure the
> >>new CPU doesn't need a new errata work around which has not been
> >>detected already. However we don't run enable() method on the new
> >>CPU for the errata work arounds already detected. This could
> >>cause the new CPU running without potential work arounds.
> >>It is upto the "enable()" method to decide if this CPU should
> >>do something about the errata.
> >>
> >>Fixes: commit 6a6efbb45b7d95c84 ("arm64: Verify CPU errata work arounds on hotplugged CPU")
> >>Cc: Will Deacon <will.deacon@....com>
> >>Cc: Mark Rutland <mark.rutland@....com>
> >>Cc: Andre Przywara <andre.przywara@....com>
> >>Cc: Catalin Marinas <catalin.marinas@....com>
> >>Cc: Dave Martin <dave.martin@....com>
> >>Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> >>---
> >>  arch/arm64/kernel/cpu_errata.c | 9 ++++++---
> >>  1 file changed, 6 insertions(+), 3 deletions(-)
> >>
> >>diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> >>index 90a9e465339c..54e41dfe41f6 100644
> >>--- a/arch/arm64/kernel/cpu_errata.c
> >>+++ b/arch/arm64/kernel/cpu_errata.c
> >>@@ -373,15 +373,18 @@ void verify_local_cpu_errata_workarounds(void)
> >>  {
> >>  	const struct arm64_cpu_capabilities *caps = arm64_errata;
> >>-	for (; caps->matches; caps++)
> >>-		if (!cpus_have_cap(caps->capability) &&
> >>-			caps->matches(caps, SCOPE_LOCAL_CPU)) {
> >>+	for (; caps->matches; caps++) {
> >>+		if (cpus_have_cap(caps->capability)) {
> >>+			if (caps->enable)
> >>+				caps->enable((void *)caps);
> >
> >Do we really need this cast?
> 
> Yes, otherwise we would be passing a "const *" where a "void *" is expected,
> and the compiler warns. Or we could simply change the prototype of the
> enable() method to accept a const capability ptr.

Hmmm, what is this argument for exactly?  cpufeature.h doesn't explain
what it is.

Does any enable method use this for anything other than a struct
arm64_cpu_capabilities const * ?  If not, it would be better to
specifiy that.

Cheers
---Dave