[ 032/108] mtd: nandsim: dont open code a do_div helper

From: Ben Hutchings
Date: Sun Jul 22 2012 - 21:47:59 EST

3.2-stable review patch. If anyone has any objections, please let me know.


From: Herton Ronaldo Krzesinski <herton.krzesinski@xxxxxxxxxxxxx>

commit 596fd46268634082314b3af1ded4612e1b7f3f03 upstream.

We don't need to open code the divide function, just use div_u64 that
already exists and do the same job. While this is a straightforward
clean up, there is more to that, the real motivation for this.

While building on a cross compiling environment in armel, using gcc
4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5), I was getting the following build

ERROR: "__aeabi_uldivmod" [drivers/mtd/nand/nandsim.ko] undefined!

After investigating with objdump and hand built assembly version
generated with the compiler, I narrowed __aeabi_uldivmod as being
generated from the divide function. When nandsim.c is built with
-fno-inline-functions-called-once, that happens when
CONFIG_DEBUG_SECTION_MISMATCH is enabled, the do_div optimization in
arch/arm/include/asm/div64.h doesn't work as expected with the open
coded divide function: even if the do_div we are using doesn't have a
constant divisor, the compiler still includes the else parts of the
optimized do_div macro, and translates the divisions there to use
__aeabi_uldivmod, instead of only calling __do_div_asm -> __do_div64 and
optimizing/removing everything else out.

So to reproduce, gcc 4.6 plus CONFIG_DEBUG_SECTION_MISMATCH=y and
CONFIG_MTD_NAND_NANDSIM=m should do it, building on armel.

After this change, the compiler does the intended thing even with
-fno-inline-functions-called-once, and optimizes out as expected the
constant handling in the optimized do_div on arm. As this also avoids a
build issue, I'm marking for Stable, as I think is applicable for this

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@xxxxxxxxxxxxx>
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Signed-off-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/mtd/nand/nandsim.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c
index 6cc8fbf..cf0cd31 100644
--- a/drivers/mtd/nand/nandsim.c
+++ b/drivers/mtd/nand/nandsim.c
@@ -28,7 +28,7 @@
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/vmalloc.h>
-#include <asm/div64.h>
+#include <linux/math64.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/string.h>
@@ -546,12 +546,6 @@ static char *get_partition_name(int i)
return kstrdup(buf, GFP_KERNEL);

-static uint64_t divide(uint64_t n, uint32_t d)
- do_div(n, d);
- return n;
* Initialize the nandsim structure.
@@ -580,7 +574,7 @@ static int init_nandsim(struct mtd_info *mtd)
ns->geom.oobsz = mtd->oobsize;
ns->geom.secsz = mtd->erasesize;
ns->geom.pgszoob = ns->geom.pgsz + ns->geom.oobsz;
- ns->geom.pgnum = divide(ns->geom.totsz, ns->geom.pgsz);
+ ns->geom.pgnum = div_u64(ns->geom.totsz, ns->geom.pgsz);
ns->geom.totszoob = ns->geom.totsz + (uint64_t)ns->geom.pgnum * ns->geom.oobsz;
ns->geom.secshift = ffs(ns->geom.secsz) - 1;
ns->geom.pgshift = chip->page_shift;
@@ -921,7 +915,7 @@ static int setup_wear_reporting(struct mtd_info *mtd)

if (!rptwear)
return 0;
- wear_eb_count = divide(mtd->size, mtd->erasesize);
+ wear_eb_count = div_u64(mtd->size, mtd->erasesize);
mem = wear_eb_count * sizeof(unsigned long);
if (mem / sizeof(unsigned long) != wear_eb_count) {
NS_ERR("Too many erase blocks for wear reporting\n");

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