From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pb0-x235.google.com ([2607:f8b0:400e:c01::235]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1WamZr-0004gg-Ub for linux-mtd@lists.infradead.org; Thu, 17 Apr 2014 13:42:08 +0000 Received: by mail-pb0-f53.google.com with SMTP id rp16so388776pbb.40 for ; Thu, 17 Apr 2014 06:41:43 -0700 (PDT) Date: Thu, 17 Apr 2014 21:41:29 +0800 From: Huang Shijie To: Gerhard Sittig Subject: Re: [PATCH] mtd: spi-nor: fix the wrong dummy value Message-ID: <20140417134127.GA3980@localhost.localdomain> References: <1397636299-2390-1-git-send-email-b32955@freescale.com> <20140416200849.GO3528@book.gsilab.sittig.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140416200849.GO3528@book.gsilab.sittig.org> Cc: marex@denx.de, Huang Shijie , computersforpeace@gmail.com, linux-mtd@lists.infradead.org, dwmw2@infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Apr 16, 2014 at 10:08:49PM +0200, Gerhard Sittig wrote: > On Wed, 2014-04-16 at 16:18 +0800, Huang Shijie wrote: > > > > The dummy cycles is actually 8 for SPI fast/dual/quad read. > > > > This patch fixes the wrong dummy value for both the spi-nor.c and m25p80.c. > > > > Signed-off-by: Huang Shijie > > --- > > drivers/mtd/devices/m25p80.c | 3 +++ > > drivers/mtd/spi-nor/spi-nor.c | 2 +- > > 2 files changed, 4 insertions(+), 1 deletions(-) > > > > diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c > > index 1557d8f..112ca8b 100644 > > --- a/drivers/mtd/devices/m25p80.c > > +++ b/drivers/mtd/devices/m25p80.c > > @@ -131,6 +131,9 @@ static int m25p80_read(struct spi_nor *nor, loff_t from, size_t len, > > int dummy = nor->read_dummy; > > int ret; > > > > + /* convert the dummy cycles to the number of byte */ > > + dummy >>= 3; > > + > > "dummy /= 8" to match the comment / commit message, and for > better mental association with a byte's width and the below > return value? The disassemble code for "int dummy = 8; dummy /= 8;" is: -------------------------------------------------- 83a6: 2308 movs r3, #8 83a8: 607b str r3, [r7, #4] 83aa: 687b ldr r3, [r7, #4] 83ac: 1dda adds r2, r3, #7 83ae: 2b00 cmp r3, #0 83b0: bfb4 ite lt 83b2: 4613 movlt r3, r2 83b4: 461b movge r3, r3 83b6: 10db asrs r3, r3, #3 83b8: 607b str r3, [r7, #4] -------------------------------------------------- The disassemble code for "int dummy = 8; dummy >>= 3;" is: -------------------------------------------------- 83a6: 2308 movs r3, #8 83a8: 607b str r3, [r7, #4] 83aa: 687b ldr r3, [r7, #4] 83ac: 10db asrs r3, r3, #3 83ae: 607b str r3, [r7, #4] -------------------------------------------------- Obviously, the "dummy >>= 3" is faster then "dummy /= 8". thanks Huang Shijie