linux-kernel - Re: [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from gic_acpi_match

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Message-ID: <ZTbCX0n2SrhUBESf@shell.armlinux.org.uk>
Date:   Mon, 23 Oct 2023 19:58:39 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 29/35] irqchip/gic-v3: Don't return errors from
 gic_acpi_match_gicc()

On Thu, Sep 14, 2023 at 04:02:23PM +0100, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:17 +0000
> James Morse <james.morse@....com> wrote:
> 
> > gic_acpi_match_gicc() is only called via gic_acpi_count_gicr_regions().
> > It should only count the number of enabled redistributors, but it
> > also tries to sanity check the GICC entry, currently returning an
> > error if the Enabled bit is set, but the gicr_base_address is zero.
> > 
> > Adding support for the online-capable bit to the sanity check
> > complicates it, for no benefit. The existing check implicitly
> > depends on gic_acpi_count_gicr_regions() previous failing to find
> > any GICR regions (as it is valid to have gicr_base_address of zero if
> > the redistributors are described via a GICR entry).
> > 
> > Instead of complicating the check, remove it. Failures that happen
> > at this point cause the irqchip not to register, meaning no irqs
> > can be requested. The kernel grinds to a panic() pretty quickly.
> > 
> > Without the check, MADT tables that exhibit this problem are still
> > caught by gic_populate_rdist(), which helpfully also prints what
> > went wrong:
> > | CPU4: mpidr 100 has no re-distributor!
> > 
> > Signed-off-by: James Morse <james.morse@....com>
> > ---
> >  drivers/irqchip/irq-gic-v3.c | 18 ++++++------------
> >  1 file changed, 6 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > index 72d3cdebdad1..0f54811262eb 100644
> > --- a/drivers/irqchip/irq-gic-v3.c
> > +++ b/drivers/irqchip/irq-gic-v3.c
> > @@ -2415,21 +2415,15 @@ static int __init gic_acpi_match_gicc(union acpi_subtable_headers *header,
> >  
> >  	/*
> >  	 * If GICC is enabled and has valid gicr base address, then it means
> > -	 * GICR base is presented via GICC
> > +	 * GICR base is presented via GICC. The redistributor is only known to
> > +	 * be accessible if the GICC is marked as enabled. If this bit is not
> > +	 * set, we'd need to add the redistributor at runtime, which isn't
> > +	 * supported.
> >  	 */
> > -	if (acpi_gicc_is_usable(gicc) && gicc->gicr_base_address) {
> > +	if (gicc->flags & ACPI_MADT_ENABLED && gicc->gicr_base_address)
> 
> Going in circles...

It does seem that way. Are you suggesting something should change here?

Thanks.

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