genirq: Implement irq reservation

Mark a range of interrupts as allocated. In the SPARSE_IRQ=n case we
need this to update the bitmap for the legacy irqs so the enumerator
via irq_get_next_irq() works.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 27 insertions, 0 deletions

diff --git a/include/linux/irq.h b/include/linux/irq.h
index cefacf928b33..096b74d5d0d7 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -400,6 +400,7 @@ static inline struct irq_2_iommu *irq_data_get_iommu(struct irq_data *d)
 
 int irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node);
 void irq_free_descs(unsigned int irq, unsigned int cnt);
+int irq_reserve_irqs(unsigned int from, unsigned int cnt);
 
 static inline int irq_alloc_desc(int node)
 {
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 2e7e94ef64da..35d9052901b9 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -464,6 +464,32 @@ err:
 }
 
 /**
+ * irq_reserve_irqs - mark irqs allocated
+ * @from:       mark from irq number
+ * @cnt:        number of irqs to mark
+ *
+ * Returns 0 on success or an appropriate error code
+ */
+int irq_reserve_irqs(unsigned int from, unsigned int cnt)
+{
+        unsigned long flags;
+        unsigned int start;
+        int ret = 0;
+
+        if (!cnt || (from + cnt) > nr_irqs)
+                return -EINVAL;
+
+        raw_spin_lock_irqsave(&sparse_irq_lock, flags);
+        start = bitmap_find_next_zero_area(allocated_irqs, nr_irqs, from, cnt, 0);
+        if (start == from)
+                bitmap_set(allocated_irqs, start, cnt);
+        else
+                ret = -EEXIST;
+        raw_spin_unlock_irqrestore(&sparse_irq_lock, flags);
+        return ret;
+}
+
+/**
  * irq_get_next_irq - get next allocated irq number
  * @offset:     where to start the search
  *