Re: [PATCH RFC v3 14/21] irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc()

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 13 Dec 2023 12:50:23 +0000
Russell King (Oracle) <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
> 
> 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@arm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> ---
>  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 98b0329b7154..ebecd4546830 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -2420,21 +2420,15 @@ 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)

I was very vague in previous review.  I think the reasons you are switching
from acpi_gicc_is_useable(gicc) to the gicc->flags & ACPI_MADT_ENABLED
needs calling out as I'm fairly sure that this point in the series at least
acpi_gicc_is_usable is same as current upstream:

static inline bool acpi_gicc_is_usable(struct acpi_madt_generic_interrupt *gicc)
{
	return gicc->flags & ACPI_MADT_ENABLED;
}

>  		acpi_data.enabled_rdists++;
> -		return 0;
> -	}
>  
> -	/*
> -	 * It's perfectly valid firmware can pass disabled GICC entry, driver
> -	 * should not treat as errors, skip the entry instead of probe fail.
> -	 */
> -	if (!acpi_gicc_is_usable(gicc))
> -		return 0;
> -
> -	return -ENODEV;
> +	return 0;
>  }
>  
>  static int __init gic_acpi_count_gicr_regions(void)