[PATCH v3 06/13] genirq: Don't mask IRQ within flow handler if IRQ is flow-masked

Valentin Schneider
2021-06-29T12:51:21Z

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