[PATCH v4 40/40] powerpc/xive: drop locking around IRQ map

[Yury Norov]

The code operates on individual bits of the bitmap, and leveraging
atomic find ops we can drop locking scheme around the map.

Signed-off-by: Yury Norov <yury.no...@gmail.com>
---
 arch/powerpc/sysdev/xive/spapr.c | 34 ++++++--------------------------
 1 file changed, 6 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/sysdev/xive/spapr.c b/arch/powerpc/sysdev/xive/spapr.c
index e45419264391..2b3b8ad75b42 100644
--- a/arch/powerpc/sysdev/xive/spapr.c
+++ b/arch/powerpc/sysdev/xive/spapr.c
@@ -17,6 +17,7 @@
 #include <linux/spinlock.h>
 #include <linux/bitmap.h>
 #include <linux/cpumask.h>
+#include <linux/find_atomic.h>
 #include <linux/mm.h>
 #include <linux/delay.h>
 #include <linux/libfdt.h>
@@ -41,7 +42,6 @@ struct xive_irq_bitmap {
        unsigned long           *bitmap;
        unsigned int            base;
        unsigned int            count;
-       spinlock_t              lock;
        struct list_head        list;
 };
 
@@ -55,7 +55,6 @@ static int __init xive_irq_bitmap_add(int base, int count)
        if (!xibm)
                return -ENOMEM;
 
-       spin_lock_init(&xibm->lock);
        xibm->base = base;
        xibm->count = count;
        xibm->bitmap = bitmap_zalloc(xibm->count, GFP_KERNEL);
@@ -81,47 +80,26 @@ static void xive_irq_bitmap_remove_all(void)
        }
 }
 
-static int __xive_irq_bitmap_alloc(struct xive_irq_bitmap *xibm)
-{
-       int irq;
-
-       irq = find_first_zero_bit(xibm->bitmap, xibm->count);
-       if (irq != xibm->count) {
-               set_bit(irq, xibm->bitmap);
-               irq += xibm->base;
-       } else {
-               irq = -ENOMEM;
-       }
-
-       return irq;
-}
-
 static int xive_irq_bitmap_alloc(void)
 {
        struct xive_irq_bitmap *xibm;
-       unsigned long flags;
-       int irq = -ENOENT;
 
        list_for_each_entry(xibm, &xive_irq_bitmaps, list) {
-               spin_lock_irqsave(&xibm->lock, flags);
-               irq = __xive_irq_bitmap_alloc(xibm);
-               spin_unlock_irqrestore(&xibm->lock, flags);
-               if (irq >= 0)
-                       break;
+               int irq = find_and_set_bit(xibm->bitmap, xibm->count);
+
+               if (irq < xibm->count)
+                       return irq + xibm->base;
        }
-       return irq;
+       return -ENOENT;
 }
 
 static void xive_irq_bitmap_free(int irq)
 {
-       unsigned long flags;
        struct xive_irq_bitmap *xibm;
 
        list_for_each_entry(xibm, &xive_irq_bitmaps, list) {
                if ((irq >= xibm->base) && (irq < xibm->base + xibm->count)) {
-                       spin_lock_irqsave(&xibm->lock, flags);
                        clear_bit(irq - xibm->base, xibm->bitmap);
-                       spin_unlock_irqrestore(&xibm->lock, flags);
                        break;
                }
        }
-- 
2.43.0