linux-kernel - Re: [PATCH v3] arm64: errata: Workaround for SI L1 downstream coherency issue

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Message-ID: <CAPTxkvRXmVB9MbPX2vkyhAnLDyJX7YviekOH=y3EcS_1e796Zg@mail.gmail.com>
Date: Thu, 15 Jan 2026 10:11:12 +0800
From: Lucas Wei <lucaswei@...gle.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Jonathan Corbet <corbet@....net>, sjadavani@...gle.com, stable@...r.kernel.org, 
	kernel-team@...roid.com, linux-arm-kernel@...ts.infradead.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, robin.murphy@....com, 
	maz@...nel.org
Subject: Re: [PATCH v3] arm64: errata: Workaround for SI L1 downstream
 coherency issue

Hi Randy,

> > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> > index 8cb3b575a031..5c0ab6bfd44a 100644
> > --- a/arch/arm64/kernel/cpu_errata.c
> > +++ b/arch/arm64/kernel/cpu_errata.c
> > @@ -141,6 +141,30 @@ has_mismatched_cache_type(const struct arm64_cpu_capabilities *entry,
> >       return (ctr_real != sys) && (ctr_raw != sys);
> >  }
> >
> > +#ifdef CONFIG_ARM64_ERRATUM_4311569
> > +static DEFINE_STATIC_KEY_FALSE(arm_si_l1_workaround_4311569);
> > +static int __init early_arm_si_l1_workaround_4311569_cfg(char *arg)
> > +{
> > +     static_branch_enable(&arm_si_l1_workaround_4311569);
> > +     pr_info("Enabling cache maintenance workaround for ARM SI-L1 erratum 4311569\n");
> > +
> > +     return 0;
> > +}
> > +early_param("arm_si_l1_workaround_4311569", early_arm_si_l1_workaround_4311569_cfg);
> > +
>
> It looks like all other errata don't use early_param() -- are they auto-detected?
> Could this one be auto-detected?

Sadly, this can't be auto-detected...

In my v2 patches, thanks Marc and Will for pointing this question out
and we don't have a reliable way to detect
errata in runtime because Linux generally doesn't need to worry about the SLC.

Robin also proposes a few feasible ways(SMCCC, top-level SoC/platform
compatible or kernel cmdline) to
enable this workaround. But, I think it would be more straightforward
to let the admin to enable this workaround via cmdline.

> > +/*
> > + * We have some earlier use cases to call cache maintenance operation functions, for example,
> > + * dcache_inval_poc() and dcache_clean_poc() in head.S, before making decision to turn on this
> > + * workaround. Since the scope of this workaround is limited to non-coherent DMA agents, its
> > + * safe to have the workaround off by default.
>
> But it's not off by default...

I think it's off by default.
Would you point me to where the workaround was enabled without cmdline?

Thanks.

 - Lucas