[RFC PATCH 1/3] genirq: Add disable_irq_nowait()

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Drivers that switch between interrupt and polled completions don't need
to wait for the mask to reach the device; the disabled state already
keeps their handler from running and a late interrupt is replayed on
enable. Add an optional irq_chip irq_mask_nowait() callback, falling
back to irq_mask(), and disable_irq_nowait() to mask through it right
away rather than lazily.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 include/linux/interrupt.h |  1 +
 include/linux/irq.h       |  4 ++++
 kernel/irq/chip.c         | 31 +++++++++++++++++++++++++++++++
 kernel/irq/internals.h    |  1 +
 kernel/irq/manage.c       | 21 +++++++++++++++++++++
 5 files changed, 58 insertions(+)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 3bf969ad8fe07..d40c992ddb8a1 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -231,6 +231,7 @@ extern void devm_free_irq(struct device *dev, unsigned int irq, void *dev_id);
 
 bool irq_has_action(unsigned int irq);
 extern void disable_irq_nosync(unsigned int irq);
+extern void disable_irq_nowait(unsigned int irq);
 extern bool disable_hardirq(unsigned int irq);
 extern void disable_irq(unsigned int irq);
 extern void disable_percpu_irq(unsigned int irq);
diff --git a/include/linux/irq.h b/include/linux/irq.h
index f485369b1b4f7..de095299f20ed 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -455,6 +455,9 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
  * @irq_disable:	disable the interrupt
  * @irq_ack:		start of a new interrupt
  * @irq_mask:		mask an interrupt source
+ * @irq_mask_nowait:	mask an interrupt source without waiting for the
+ *			hardware to acknowledge it (optional, falls back to
+ *			@irq_mask)
  * @irq_mask_ack:	ack and mask an interrupt source
  * @irq_unmask:		unmask an interrupt source
  * @irq_eoi:		end of interrupt
@@ -505,6 +508,7 @@ struct irq_chip {
 
 	void		(*irq_ack)(struct irq_data *data);
 	void		(*irq_mask)(struct irq_data *data);
+	void		(*irq_mask_nowait)(struct irq_data *data);
 	void		(*irq_mask_ack)(struct irq_data *data);
 	void		(*irq_unmask)(struct irq_data *data);
 	void		(*irq_eoi)(struct irq_data *data);
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index de754db414d1d..4e76f025b5f68 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -399,6 +399,37 @@ void irq_disable(struct irq_desc *desc)
 	__irq_disable(desc, irq_settings_disable_unlazy(desc));
 }
 
+static void mask_irq_nowait(struct irq_desc *desc)
+{
+	if (irqd_irq_masked(&desc->irq_data))
+		return;
+
+	if (desc->irq_data.chip->irq_mask_nowait) {
+		desc->irq_data.chip->irq_mask_nowait(&desc->irq_data);
+		irq_state_set_masked(desc);
+	} else {
+		mask_irq(desc);
+	}
+}
+
+/**
+ * irq_disable_nowait - Mark interrupt disabled and mask it without waiting
+ * @desc:	irq descriptor which should be disabled
+ *
+ * Like irq_disable() with lazy disable turned off, but the hardware may
+ * still deliver an interrupt after this returns. The flow handler deals
+ * with that the same way it does for a lazily disabled interrupt.
+ */
+void irq_disable_nowait(struct irq_desc *desc)
+{
+	if (desc->irq_data.chip->irq_disable) {
+		__irq_disable(desc, true);
+		return;
+	}
+	irq_state_set_disabled(desc);
+	mask_irq_nowait(desc);
+}
+
 void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu)
 {
 	if (desc->irq_data.chip->irq_enable)
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 0ce21dd454047..3ba13932ba831 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -98,6 +98,7 @@ extern void irq_startup_managed(struct irq_desc *desc);
 extern void irq_shutdown(struct irq_desc *desc);
 extern void irq_shutdown_and_deactivate(struct irq_desc *desc);
 extern void irq_disable(struct irq_desc *desc);
+extern void irq_disable_nowait(struct irq_desc *desc);
 extern void irq_percpu_enable(struct irq_desc *desc, unsigned int cpu);
 extern void irq_percpu_disable(struct irq_desc *desc, unsigned int cpu);
 extern void mask_irq(struct irq_desc *desc);
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 57eff26fa646a..7a4d7f1024133 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -705,6 +705,27 @@ void disable_irq_nosync(unsigned int irq)
 }
 EXPORT_SYMBOL(disable_irq_nosync);
 
+/**
+ * disable_irq_nowait - mask an irq without waiting for the hardware
+ * @irq: Interrupt to disable
+ *
+ * Like disable_irq_nosync(), but masks the interrupt at the chip right away
+ * instead of lazily, and does not wait for the hardware to acknowledge the
+ * mask. An interrupt that still arrives is held pending and replayed by
+ * enable_irq(). Use this when an extra interrupt is cheaper than flushing
+ * the mask, e.g. switching from interrupts to polling.
+ *
+ * This function may be called from IRQ context.
+ */
+void disable_irq_nowait(unsigned int irq)
+{
+	scoped_irqdesc_get_and_buslock(irq, IRQ_GET_DESC_CHECK_GLOBAL) {
+		if (!scoped_irqdesc->depth++)
+			irq_disable_nowait(scoped_irqdesc);
+	}
+}
+EXPORT_SYMBOL_GPL(disable_irq_nowait);
+
 /**
  * disable_irq - disable an irq and wait for completion
  * @irq: Interrupt to disable
-- 
2.52.0