[RFC PATCH v2 06/10] genirq: Don't mask IRQ within flow handler if IRQ is flow-masked

[Valentin Schneider <valentin.schneider@arm.com>]

mask_irq() lets an IRQ with IRQD_IRQ_FLOW_MASKED set be further masked via
chip->irq_mask(). This is necessary for unhandled IRQs as we want to keep
them masked beyond eoi_irq() (which clears IRQD_IRQ_FLOW_MASKED).

This is however not necessary in paths that do end up handling the IRQ and
are bounded by a final eoi_irq() - this is the case for chips with
IRQCHIP_AUTOMASKS_FLOW and IRQCHIP_EOI_THREADED.

Make handle_strict_flow_irq() leverage IRQCHIP_AUTOMASKS_FLOW and issue an
ack_irq() rather than a mask_ack_irq() when possible.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
 kernel/irq/chip.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 699e70b51aae..c2ca6b748987 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -896,6 +896,12 @@ void handle_edge_eoi_irq(struct irq_desc *desc)
 }
 #endif
 
+/*
+ * AUTOMASKS_FLOW tells us ack/eoi handle the masking, EOI_THREADED tells us
+ * that masking will persist until irq_finalize_oneshot()
+ */
+#define ONESHOT_AUTOMASK_FLAGS (IRQCHIP_AUTOMASKS_FLOW | IRQCHIP_EOI_THREADED)
+
 /**
  *	handle_strict_flow_irq - irq handler for strict controllers
  *	@desc:	the interrupt description structure for this irq
@@ -909,10 +915,9 @@ void handle_strict_flow_irq(struct irq_desc *desc)
 	struct irq_chip *chip = desc->irq_data.chip;
 
 	raw_spin_lock(&desc->lock);
-	mask_ack_irq(desc);
 
 	if (!irq_may_run(desc))
-		goto out;
+		goto out_mask;
 
 	desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);
 
@@ -922,10 +927,20 @@ void handle_strict_flow_irq(struct irq_desc *desc)
 	 */
 	if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {
 		desc->istate |= IRQS_PENDING;
-		goto out;
+		goto out_mask;
 	}
 
 	kstat_incr_irqs_this_cpu(desc);
+	/*
+	 * Masking is required if IRQ is ONESHOT and we can't rely on the
+	 * flow-masking persisting down to irq_finalize_oneshot()
+	 * (in the IRQ thread).
+	 */
+	if ((desc->istate & IRQS_ONESHOT) &&
+	    ((chip->flags & ONESHOT_AUTOMASK_FLAGS) != ONESHOT_AUTOMASK_FLAGS))
+		mask_ack_irq(desc);
+	else
+		ack_irq(desc);
 
 	handle_irq_event(desc);
 
@@ -933,7 +948,8 @@ void handle_strict_flow_irq(struct irq_desc *desc)
 
 	raw_spin_unlock(&desc->lock);
 	return;
-out:
+out_mask:
+	mask_ack_irq(desc);
 	/*
 	 * XXX: this is where IRQCHIP_EOI_IF_HANDLED would be checked, but
 	 * it's conceptually incompatible with this handler (it breaks the
-- 
2.25.1