From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 15 Aug 2016 09:48:49 +0000 (+0100)
Subject: drm/i915: Add fetch_and_zero() macro
X-Git-Tag: v4.9-rc1~41^2~36^2~82
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=78ef2d9abad6da3f94489148b4e08359dd2fb4fe;p=karo-tx-linux.git

drm/i915: Add fetch_and_zero() macro

A simple little macro to clear a pointer and return the old value. This
is useful for writing

	value = *ptr;
	if (!value)
		return;

	*ptr = 0;
	...
	free(value);

in a slightly more concise form:

	value = fetch_and_zero(ptr);
	if (!value)
		return;

	...
	free(value);

with the idea that this establishes a pattern that may be extended for
atomic use (using xchg or cmpxchg) i.e. atomic_fetch_and_zero() and
similar to llist.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-10-git-send-email-chris@chris-wilson.co.uk
---

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 25b1e6c010d5..855833a6306a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3920,4 +3920,10 @@ bool i915_memcpy_from_wc(void *dst, const void *src, unsigned long len);
 #define ptr_pack_bits(ptr, bits)					\
 	((typeof(ptr))((unsigned long)(ptr) | (bits)))
 
+#define fetch_and_zero(ptr) ({						\
+	typeof(*ptr) __T = *(ptr);					\
+	*(ptr) = (typeof(*ptr))0;					\
+	__T;								\
+})
+
 #endif