genirq: Introduce IRQD_SINGLE_TARGET flag

Many interrupt chips allow only a single CPU as interrupt target. The core
code has no knowledge about that. That's unfortunate as it could avoid
trying to readd a newly online CPU to the effective affinity mask.

Add the status flag and the necessary accessors.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235447.352343969@linutronix.de

include/linux/irq.h

@@ -209,6 +209,7 @@ struct irq_data {
  * IRQD_IRQ_STARTED		- Startup state of the interrupt
  * IRQD_MANAGED_SHUTDOWN	- Interrupt was shutdown due to empty affinity
  *				  mask. Applies only to affinity managed irqs.
+ * IRQD_SINGLE_TARGET		- IRQ allows only a single affinity target
  */
 enum {
 	IRQD_TRIGGER_MASK		= 0xf,
@@ -228,6 +229,7 @@ enum {
 	IRQD_AFFINITY_MANAGED		= (1 << 21),
 	IRQD_IRQ_STARTED		= (1 << 22),
 	IRQD_MANAGED_SHUTDOWN		= (1 << 23),
+	IRQD_SINGLE_TARGET		= (1 << 24),
 };
 
 #define __irqd_to_state(d) ACCESS_PRIVATE((d)->common, state_use_accessors)
@@ -276,6 +278,20 @@ static inline bool irqd_is_level_type(struct irq_data *d)
 	return __irqd_to_state(d) & IRQD_LEVEL;
 }
 
+/*
+ * Must only be called of irqchip.irq_set_affinity() or low level
+ * hieararchy domain allocation functions.
+ */
+static inline void irqd_set_single_target(struct irq_data *d)
+{
+	__irqd_to_state(d) |= IRQD_SINGLE_TARGET;
+}
+
+static inline bool irqd_is_single_target(struct irq_data *d)
+{
+	return __irqd_to_state(d) & IRQD_SINGLE_TARGET;
+}
+
 static inline bool irqd_is_wakeup_set(struct irq_data *d)
 {
 	return __irqd_to_state(d) & IRQD_WAKEUP_STATE;

kernel/irq/debugfs.c

@@ -105,6 +105,7 @@ static const struct irq_bit_descr irqdata_states[] = {
 	BIT_MASK_DESCR(IRQD_PER_CPU),
 	BIT_MASK_DESCR(IRQD_NO_BALANCING),
 
+	BIT_MASK_DESCR(IRQD_SINGLE_TARGET),
 	BIT_MASK_DESCR(IRQD_MOVE_PCNTXT),
 	BIT_MASK_DESCR(IRQD_AFFINITY_SET),
 	BIT_MASK_DESCR(IRQD_SETAFFINITY_PENDING),