[RFC PATCH 01/10] genirq: Add chip flag to denote automatic IRQ (un)masking

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

Some IRQ chips such as the Arm GICs automagically mask / unmask an
IRQ during the handling of said IRQ. This renders further mask / unmask
operations within the flow handlers redundant, which we do want to leverage
as masking by itself is not cheap (Distributor access via MMIO for GICs).

This is different from having a chip->irq_mask_ack() callback as this
masking is:
- inherent to the chip->irq_ack() and *cannot* be omitted
- a *different* masking state than chip->irq_mask() (chip->irq_mask() is
  idempotent, chip->irq_ack() really isn't)

Add a chip flag, IRQCHIP_AUTOMASKS_FLOW, to denote chips with such
behaviour. Add a new IRQ data flag, IRQD_IRQ_FLOW_MASKED, to keep this
flow-induced mask state separate from regular mask / unmask operations
(IRQD_IRQ_MASKED).

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
 include/linux/irq.h    | 10 ++++++++++
 kernel/irq/chip.c      |  5 +++++
 kernel/irq/debugfs.c   |  2 ++
 kernel/irq/internals.h |  5 +++++
 4 files changed, 22 insertions(+)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index bee82809107c..580b1b6b1799 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -219,6 +219,8 @@ struct irq_data {
  *				  irq_chip::irq_set_affinity() when deactivated.
  * IRQD_IRQ_ENABLED_ON_SUSPEND	- Interrupt is enabled on suspend by irq pm if
  *				  irqchip have flag IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND set.
+ * IRQD_IRQ_FLOW_MASKED         - Interrupt is masked by ACK. Only EOI can
+ *                                clear this.
  */
 enum {
 	IRQD_TRIGGER_MASK		= 0xf,
@@ -245,6 +247,7 @@ enum {
 	IRQD_HANDLE_ENFORCE_IRQCTX	= (1 << 28),
 	IRQD_AFFINITY_ON_ACTIVATE	= (1 << 29),
 	IRQD_IRQ_ENABLED_ON_SUSPEND	= (1 << 30),
+	IRQD_IRQ_FLOW_MASKED            = (1 << 31),
 };
 
 #define __irqd_to_state(d) ACCESS_PRIVATE((d)->common, state_use_accessors)
@@ -349,6 +352,11 @@ static inline bool irqd_irq_masked(struct irq_data *d)
 	return __irqd_to_state(d) & IRQD_IRQ_MASKED;
 }
 
+static inline bool irqd_irq_flow_masked(struct irq_data *d)
+{
+	return __irqd_to_state(d) & IRQD_IRQ_FLOW_MASKED;
+}
+
 static inline bool irqd_irq_inprogress(struct irq_data *d)
 {
 	return __irqd_to_state(d) & IRQD_IRQ_INPROGRESS;
@@ -567,6 +575,7 @@ struct irq_chip {
  * IRQCHIP_SUPPORTS_NMI:              Chip can deliver NMIs, only for root irqchips
  * IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND:  Invokes __enable_irq()/__disable_irq() for wake irqs
  *                                    in the suspend path if they are in disabled state
+ * IRQCHIP_AUTOMASKS_FLOW:            chip->ack() masks and chip->eoi() unmasks
  */
 enum {
 	IRQCHIP_SET_TYPE_MASKED			= (1 <<  0),
@@ -579,6 +588,7 @@ enum {
 	IRQCHIP_SUPPORTS_LEVEL_MSI		= (1 <<  7),
 	IRQCHIP_SUPPORTS_NMI			= (1 <<  8),
 	IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND	= (1 <<  9),
+	IRQCHIP_AUTOMASKS_FLOW                  = (1 <<  10),
 };
 
 #include <linux/irqdesc.h>
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index 8cc8e5713287..18c3b0e1568a 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -173,6 +173,11 @@ static void irq_state_clr_masked(struct irq_desc *desc)
 	irqd_clear(&desc->irq_data, IRQD_IRQ_MASKED);
 }
 
+static void irq_state_clr_flow_masked(struct irq_desc *desc)
+{
+	irqd_clear(&desc->irq_data, IRQD_IRQ_FLOW_MASKED);
+}
+
 static void irq_state_clr_started(struct irq_desc *desc)
 {
 	irqd_clear(&desc->irq_data, IRQD_IRQ_STARTED);
diff --git a/kernel/irq/debugfs.c b/kernel/irq/debugfs.c
index e4cff358b437..3ae83622d701 100644
--- a/kernel/irq/debugfs.c
+++ b/kernel/irq/debugfs.c
@@ -58,6 +58,7 @@ static const struct irq_bit_descr irqchip_flags[] = {
 	BIT_MASK_DESCR(IRQCHIP_SUPPORTS_LEVEL_MSI),
 	BIT_MASK_DESCR(IRQCHIP_SUPPORTS_NMI),
 	BIT_MASK_DESCR(IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND),
+	BIT_MASK_DESCR(IRQCHIP_AUTOMASKS_FLOW),
 };
 
 static void
@@ -103,6 +104,7 @@ static const struct irq_bit_descr irqdata_states[] = {
 	BIT_MASK_DESCR(IRQD_IRQ_STARTED),
 	BIT_MASK_DESCR(IRQD_IRQ_DISABLED),
 	BIT_MASK_DESCR(IRQD_IRQ_MASKED),
+	BIT_MASK_DESCR(IRQD_IRQ_FLOW_MASKED),
 	BIT_MASK_DESCR(IRQD_IRQ_INPROGRESS),
 
 	BIT_MASK_DESCR(IRQD_PER_CPU),
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 54363527feea..b6c1cceddec0 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -245,6 +245,11 @@ static inline void irq_state_set_masked(struct irq_desc *desc)
 	irqd_set(&desc->irq_data, IRQD_IRQ_MASKED);
 }
 
+static inline void irq_state_set_flow_masked(struct irq_desc *desc)
+{
+	irqd_set(&desc->irq_data, IRQD_IRQ_FLOW_MASKED);
+}
+
 #undef __irqd_to_state
 
 static inline void __kstat_incr_irqs_this_cpu(struct irq_desc *desc)
-- 
2.25.1