genirq: Allow interrupts to be excluded from /proc/interrupts

A number of architectures implement IPI statistics directly,
duplicating the core kstat_irqs accounting. As we move IPIs to
being actual IRQs, we would end-up with a confusing display
in /proc/interrupts (where the IPIs would appear twice).

In order to solve this, allow interrupts to be flagged as
"hidden", which excludes them from /proc/interrupts.
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

include/linux/irq.h

@@ -71,6 +71,7 @@ enum irqchip_irq_state;
  *				  it from the spurious interrupt detection
  *				  mechanism and from core side polling.
  * IRQ_DISABLE_UNLAZY		- Disable lazy irq disable
+ * IRQ_HIDDEN			- Don't show up in /proc/interrupts
  */
 enum {
 	IRQ_TYPE_NONE		= 0x00000000,
@@ -97,13 +98,14 @@ enum {
 	IRQ_PER_CPU_DEVID	= (1 << 17),
 	IRQ_IS_POLLED		= (1 << 18),
 	IRQ_DISABLE_UNLAZY	= (1 << 19),
+	IRQ_HIDDEN		= (1 << 20),
 };
 
 #define IRQF_MODIFY_MASK	\
 	(IRQ_TYPE_SENSE_MASK | IRQ_NOPROBE | IRQ_NOREQUEST | \
 	 IRQ_NOAUTOEN | IRQ_MOVE_PCNTXT | IRQ_LEVEL | IRQ_NO_BALANCING | \
 	 IRQ_PER_CPU | IRQ_NESTED_THREAD | IRQ_NOTHREAD | IRQ_PER_CPU_DEVID | \
-	 IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY)
+	 IRQ_IS_POLLED | IRQ_DISABLE_UNLAZY | IRQ_HIDDEN)
 
 #define IRQ_NO_BALANCING_MASK	(IRQ_PER_CPU | IRQ_NO_BALANCING)
 

kernel/irq/debugfs.c

@@ -136,6 +136,7 @@ static const struct irq_bit_descr irqdesc_states[] = {
 	BIT_MASK_DESCR(_IRQ_PER_CPU_DEVID),
 	BIT_MASK_DESCR(_IRQ_IS_POLLED),
 	BIT_MASK_DESCR(_IRQ_DISABLE_UNLAZY),
+	BIT_MASK_DESCR(_IRQ_HIDDEN),
 };
 
 static const struct irq_bit_descr irqdesc_istates[] = {

kernel/irq/proc.c

@@ -485,7 +485,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
 	rcu_read_lock();
 	desc = irq_to_desc(i);
-	if (!desc)
+	if (!desc || irq_settings_is_hidden(desc))
 		goto outsparse;
 
 	if (desc->kstat_irqs)

kernel/irq/settings.h

@@ -17,6 +17,7 @@ enum {
 	_IRQ_PER_CPU_DEVID	= IRQ_PER_CPU_DEVID,
 	_IRQ_IS_POLLED		= IRQ_IS_POLLED,
 	_IRQ_DISABLE_UNLAZY	= IRQ_DISABLE_UNLAZY,
+	_IRQ_HIDDEN		= IRQ_HIDDEN,
 	_IRQF_MODIFY_MASK	= IRQF_MODIFY_MASK,
 };
 
@@ -31,6 +32,7 @@ enum {
 #define IRQ_PER_CPU_DEVID	GOT_YOU_MORON
 #define IRQ_IS_POLLED		GOT_YOU_MORON
 #define IRQ_DISABLE_UNLAZY	GOT_YOU_MORON
+#define IRQ_HIDDEN		GOT_YOU_MORON
 #undef IRQF_MODIFY_MASK
 #define IRQF_MODIFY_MASK	GOT_YOU_MORON
 
@@ -167,3 +169,8 @@ static inline void irq_settings_clr_disable_unlazy(struct irq_desc *desc)
 {
 	desc->status_use_accessors &= ~_IRQ_DISABLE_UNLAZY;
 }
+
+static inline bool irq_settings_is_hidden(struct irq_desc *desc)
+{
+	return desc->status_use_accessors & _IRQ_HIDDEN;
+}