Subject: Re: [RFC PATCH v2 09/10] irqchip/gic: Convert to handle_strict_flow_irq()

From: Marc Zyngier <[email-masked]>
Date: Thu, 27 May 2021 13:21:38 +0100

On Tue, 25 May 2021 18:32:54 +0100,
Valentin Schneider <[email-masked]> wrote:
> 
> Now that the proper infrastructure is in place, convert the irq-gic chip to
> use handle_strict_flow_irq() along with IRQCHIP_AUTOMASKS_FLOW.
> 
> For EOImode=1, the Priority Drop is moved from gic_handle_irq() into
> chip->irq_ack(). This effectively pushes the EOI write down into
> ->handle_irq(), but doesn't change its ordering wrt the irqaction
> handling.
> 
> The EOImode=1 irqchip also gains IRQCHIP_EOI_THREADED, which allows the
> ->irq_eoi() call to be deferred to the tail of ONESHOT IRQ threads. This
> means a threaded ONESHOT IRQ can now be handled entirely without a single
> chip->irq_mask() call.
> 
> EOImode=0 handling remains unchanged.
> 
> Signed-off-by: Valentin Schneider <[email-masked]>
> ---
>  drivers/irqchip/irq-gic.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index b1d9c22caf2e..4919478c3e41 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -344,8 +344,6 @@ static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
>  		if (unlikely(irqnr >= 1020))
>  			break;
>  
> -		if (static_branch_likely(&supports_deactivate_key))
> -			writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);
>  		isb();
>  
>  		/*
> @@ -1012,7 +1010,9 @@ static int gic_irq_domain_map(struct irq_domain *d, unsigned int irq,
>  		break;
>  	default:
>  		irq_domain_set_info(d, irq, hw, &gic->chip, d->host_data,
> -				    handle_fasteoi_irq, NULL, NULL);
> +				    static_branch_likely(&supports_deactivate_key) ?
> +				    handle_strict_flow_irq : handle_fasteoi_irq,
> +				    NULL, NULL);
>  		irq_set_probe(irq);
>  		irqd_set_single_target(irqd);
>  		break;
> @@ -1116,8 +1116,16 @@ static void gic_init_chip(struct gic_chip_data *gic, struct device *dev,
>  
>  	if (use_eoimode1) {
>  		gic->chip.irq_mask = gic_eoimode1_mask_irq;
> +		gic->chip.irq_ack = gic_eoi_irq;
>  		gic->chip.irq_eoi = gic_eoimode1_eoi_irq;
>  		gic->chip.irq_set_vcpu_affinity = gic_irq_set_vcpu_affinity;
> +
> +		/*
> +		 * eoimode0 shouldn't expose FLOW_MASK because the priority
> +		 * drop is undissociable from the deactivation, and we do need
> +		 * the priority drop to happen within the flow handler.
> +		 */
> +		gic->chip.flags |= IRQCHIP_AUTOMASKS_FLOW | IRQCHIP_EOI_THREADED;
>  	}
>  
>  	if (gic == &gic_data[0]) {

How about GICv2M, GICv3-MBI, and the collection of widget that build a
domain on top of a GIC domain? I'm worried that they now all need
updating one way or another...

	M.

-- 
Without deviation from the norm, progress is not possible.

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