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 <redacted>
---
 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]) {