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

[Valentin Schneider]

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.schnei...@arm.com>
---
 kernel/irq/chip.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 6c033b0044cb..1add0b4f0662 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -909,10 +909,9 @@ 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 +921,21 @@ 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 & IRQCHIP_AUTOMASKS_FLOW) ||
+            !(chip->flags & IRQCHIP_EOI_THREADED)))
+               mask_ack_irq(desc);
+       else
+               ack_irq(desc);
 
        handle_irq_event(desc);
 
@@ -933,7 +943,8 @@ 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