Re: [PATCH] irqchip/gic: Simplify Maintenance Interrupt ACPI parsing

[Radu Rendec <radu@rendec.net>]

On Sat, 2026-07-25 at 16:59 +0100, Marc Zyngier wrote:
> The ACPI spec describes the vgic Maintenance Interrupt with attributes
> indicating whether the signalling is Level or Edge. While this
> superficially looks like a sensible thing to do, it doesn't actually
> make much sense.
> 
> By construction, this interrupt is Level, and cannot be anything
> else, as the hypervisor actively needs to interact with the vgic
> for the level to drop. This indicates a state, and not an event.
> 
> Get rid of this nonsense, always register the corresponding GSI as
> Level, and let the user know that they run on quality FW should
> the interrupt be advertised as Edge.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  drivers/irqchip/irq-gic-v3.c | 10 +++-------
>  drivers/irqchip/irq-gic.c    |  8 ++++----
>  2 files changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 99444a1b2ffa2..22ecd28a491a8 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -2279,7 +2279,6 @@ static struct
>  	bool single_redist;
>  	int enabled_rdists;
>  	u32 maint_irq;
> -	int maint_irq_mode;
>  	phys_addr_t vcpu_base;
>  } acpi_data __initdata;
>  
> @@ -2457,21 +2456,19 @@ static int __init gic_acpi_parse_virt_madt_gicc(union acpi_subtable_headers *hea
>  {
>  	struct acpi_madt_generic_interrupt *gicc =
>  		(struct acpi_madt_generic_interrupt *)header;
> -	int maint_irq_mode;
>  	static int first_madt = true;
>  
>  	if (!(gicc->flags &
>  	      (ACPI_MADT_ENABLED | ACPI_MADT_GICC_ONLINE_CAPABLE)))
>  		return 0;
>  
> -	maint_irq_mode = (gicc->flags & ACPI_MADT_VGIC_IRQ_MODE) ?
> -		ACPI_EDGE_SENSITIVE : ACPI_LEVEL_SENSITIVE;
> +	if (gicc->flags & ACPI_MADT_VGIC_IRQ_MODE)
> +		pr_warn_once(FW_BUG "MI wrongly advertised as Edge-triggered\n");
>  
>  	if (first_madt) {
>  		first_madt = false;
>  
>  		acpi_data.maint_irq = gicc->vgic_interrupt;
> -		acpi_data.maint_irq_mode = maint_irq_mode;
>  		acpi_data.vcpu_base = gicc->gicv_base_address;
>  
>  		return 0;
> @@ -2481,7 +2478,6 @@ static int __init gic_acpi_parse_virt_madt_gicc(union acpi_subtable_headers *hea
>  	 * The maintenance interrupt and GICV should be the same for every CPU
>  	 */
>  	if ((acpi_data.maint_irq != gicc->vgic_interrupt) ||
> -	    (acpi_data.maint_irq_mode != maint_irq_mode) ||
>  	    (acpi_data.vcpu_base != gicc->gicv_base_address))
>  		return -EINVAL;
>  
> @@ -2514,7 +2510,7 @@ static void __init gic_acpi_setup_kvm_info(void)
>  	gic_v3_kvm_info.type = GIC_V3;
>  
>  	irq = acpi_register_gsi(NULL, acpi_data.maint_irq,
> -				acpi_data.maint_irq_mode,
> +				ACPI_LEVEL_SENSITIVE,
>  				ACPI_ACTIVE_HIGH);
>  	if (irq <= 0)
>  		return;
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index ec70c84e9f91d..74bda5e246345 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -1527,7 +1527,6 @@ static struct
>  {
>  	phys_addr_t cpu_phys_base;
>  	u32 maint_irq;
> -	int maint_irq_mode;
>  	phys_addr_t vctrl_base;
>  	phys_addr_t vcpu_base;
>  } acpi_data __initdata;
> @@ -1553,10 +1552,11 @@ gic_acpi_parse_madt_cpu(union acpi_subtable_headers *header,
>  	if (cpu_base_assigned && gic_cpu_base != acpi_data.cpu_phys_base)
>  		return -EINVAL;
>  
> +	if (processor->flags & ACPI_MADT_VGIC_IRQ_MODE)
> +		pr_warn_once(FW_BUG "MI wrongly advertised as Edge-triggered\n");
> +
>  	acpi_data.cpu_phys_base = gic_cpu_base;
>  	acpi_data.maint_irq = processor->vgic_interrupt;
> -	acpi_data.maint_irq_mode = (processor->flags & ACPI_MADT_VGIC_IRQ_MODE) ?
> -				    ACPI_EDGE_SENSITIVE : ACPI_LEVEL_SENSITIVE;
>  	acpi_data.vctrl_base = processor->gich_base_address;
>  	acpi_data.vcpu_base = processor->gicv_base_address;
>  
> @@ -1616,7 +1616,7 @@ static void __init gic_acpi_setup_kvm_info(void)
>  	vcpu_res->end = vcpu_res->start + ACPI_GICV2_VCPU_MEM_SIZE - 1;
>  
>  	irq = acpi_register_gsi(NULL, acpi_data.maint_irq,
> -				acpi_data.maint_irq_mode,
> +				ACPI_LEVEL_SENSITIVE,
>  				ACPI_ACTIVE_HIGH);
>  	if (irq <= 0)
>  		return;

Reviewed-by: Radu Rendec <radu@rendec.net>