linux-kernel - [RFC][PATCH] kernel.h: Add generic roundup

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Date:   Thu, 23 May 2019 10:00:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Ben Skeggs <bskeggs@...hat.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [RFC][PATCH] kernel.h: Add generic roundup_64() macro


From: Steven Rostedt (VMware) <rostedt@...dmis.org>

In discussing a build failure on x86_32 due to the use of roundup() on
a 64 bit number, I realized that there's no generic equivalent
roundup_64(). It is implemented in two separate places in the kernel,
but there really should be just one that all can use.

Although the other implementations are a static inline function, this
implementation is a macro to allow the use of typeof(x) to denote the
type that is being used. If the build is on a 64 bit machine, then the
roundup_64() macro will just default back to roundup(). But for 32 bit
machines, it will use the version that is will not cause issues with
dividing a 64 bit number on a 32 bit machine.

Link: http://lkml.kernel.org/r/20190522145450.25ff483d@gandalf.local.home

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 34a998012bf6..cdacfe1f732c 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -143,14 +143,6 @@ nouveau_bo_del_ttm(struct ttm_buffer_object *bo)
 	kfree(nvbo);
 }
 
-static inline u64
-roundup_64(u64 x, u32 y)
-{
-	x += y - 1;
-	do_div(x, y);
-	return x * y;
-}
-
 static void
 nouveau_bo_fixup_align(struct nouveau_bo *nvbo, u32 flags,
 		       int *align, u64 *size)
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index edbd5a210df2..13de9d49bd52 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -207,13 +207,6 @@ static inline xfs_dev_t linux_to_xfs_dev_t(dev_t dev)
 #define xfs_sort(a,n,s,fn)	sort(a,n,s,fn,NULL)
 #define xfs_stack_trace()	dump_stack()
 
-static inline uint64_t roundup_64(uint64_t x, uint32_t y)
-{
-	x += y - 1;
-	do_div(x, y);
-	return x * y;
-}
-
 static inline uint64_t howmany_64(uint64_t x, uint32_t y)
 {
 	x += y - 1;
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 74b1ee9027f5..cd0063629357 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -115,6 +115,20 @@
 	(((x) + (__y - 1)) / __y) * __y;		\
 }							\
 )
+
+#if BITS_PER_LONG == 32
+# define roundup_64(x, y) (				\
+{							\
+	typeof(y) __y = y;				\
+	typeof(x) __x = (x) + (__y - 1);		\
+	do_div(__x, __y);				\
+	__x * __y;					\
+}							\
+)
+#else
+# define roundup_64(x, y)	roundup(x, y)
+#endif
+
 /**
  * rounddown - round down to next specified multiple
  * @x: the value to round