From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753643Ab2GWBsF (ORCPT ); Sun, 22 Jul 2012 21:48:05 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:54472 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753601Ab2GWBnq (ORCPT ); Sun, 22 Jul 2012 21:43:46 -0400 Message-Id: <20120723010656.351850727@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Mon, 23 Jul 2012 02:07:23 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Herton Ronaldo Krzesinski , Nicolas Pitre , Artem Bityutskiy , David Woodhouse Subject: [ 032/108] mtd: nandsim: dont open code a do_div helper In-Reply-To: <20120723010651.408577075@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Herton Ronaldo Krzesinski 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: 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 case. Signed-off-by: Herton Ronaldo Krzesinski Acked-by: Nicolas Pitre Signed-off-by: Artem Bityutskiy Signed-off-by: David Woodhouse Signed-off-by: Ben Hutchings --- 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 #include #include -#include +#include #include #include #include @@ -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");