Re: [PATCH 1/3] arm64: Disable GiC priorities on Mediatek devices w/ firmware issues

[Will Deacon <will@kernel.org>]

On Mon, Oct 30, 2023 at 04:19:55PM -0700, Doug Anderson wrote:
> On Wed, Oct 18, 2023 at 4:01 AM Mark Rutland <mark.rutland@arm.com> wrote:
> > On Fri, Oct 06, 2023 at 03:15:51PM -0700, Douglas Anderson wrote:
> > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > index 2806a2850e78..e35efab8efa9 100644
> > > --- a/arch/arm64/kernel/cpufeature.c
> > > +++ b/arch/arm64/kernel/cpufeature.c
> > > @@ -2094,9 +2094,30 @@ static int __init early_enable_pseudo_nmi(char *p)
> > >  }
> > >  early_param("irqchip.gicv3_pseudo_nmi", early_enable_pseudo_nmi);
> > >
> > > +static bool are_gic_priorities_broken(void)
> > > +{
> > > +     bool is_broken = false;
> > > +     struct device_node *np;
> > > +
> > > +     /*
> > > +      * Detect broken Mediatek firmware that doesn't properly save and
> > > +      * restore GIC priorities.
> > > +      */
> > > +     np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> > > +     if (np) {
> > > +             is_broken = of_property_read_bool(np, "mediatek,broken-save-restore-fw");
> > > +             of_node_put(np);
> > > +     }
> > > +
> > > +     return is_broken;
> > > +}
> >
> > I'm definitely in favour of detecting this in the cpucap, but I think it'd be
> > better to parse the DT once on the boot CPU rather than on each CPU every time
> > it's brought up.
> >
> > I think if we add something like:
> >
> > #ifdef CONFIG_ARM64_PSEUDO_NMI
> > static void detect_system_supports_pseudo_nmi(void)
> > {
> >         struct device_node *np;
> >
> >         if (!enable_pseudo_nmi)
> >                 return;
> >
> >         /*
> >          * Detect broken Mediatek firmware that doesn't properly save and
> >          * restore GIC priorities.
> >          */
> >         np = of_find_compatible_node(NULL, NULL, "arm,gic-v3");
> >         if (np && of_property_read_bool(np, "mediatek,broken-save-restore-fw")) {
> >                 pr_info("Pseudo-NMI disabled due to Mediatek Chromebook GICR save problem");
> >                 enable_pseudo_nmi = false;
> >         }
> >         of_node_put(np);
> > }
> > #endif /* CONFIG_ARM64_PSEUDO_NMI */
> > static inline void detect_system_supports_pseudo_nmi(void) { }
> > #endif
> >
> > ... then we can call that from init_cpu_features() before we call
> > setup_boot_cpu_capabilities(), and then the existing logic in
> > can_use_gic_priorities() should just work as that returns the value of
> > enable_pseudo_nmi.
> >
> > Note: of_node_put(NULL) does nothing, like kfree(NULL), so it's fine for that
> > to be called in the !np case.
> >
> > Would you be happy to fold that in? I'm happy with a Suggested-by tag if so. :)
> 
> Yup, that looks good to me and I can fold it in (fixing a few nits
> like missing "\n" and adding __init to the function). I'll wait to get
> maintainers opinions on whether to fold patch #3 in here and then send
> a v2.

No preference from me; I assume this stuff's all going in together anyway.

Will

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