From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934740AbbKSXTD (ORCPT ); Thu, 19 Nov 2015 18:19:03 -0500 Received: from mail-pa0-f52.google.com ([209.85.220.52]:34088 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758500AbbKSXTB (ORCPT ); Thu, 19 Nov 2015 18:19:01 -0500 Date: Thu, 19 Nov 2015 15:18:57 -0800 From: Brian Norris To: Michal Suchanek Cc: Hou Zhiqiang , shijie.huang@intel.com, David Woodhouse , Han Xu , =?utf-8?B?UmFmYcWCIE1pxYJlY2tp?= , Huang Shijie , Ben Hutchings , Marek Vasut , Gabor Juhos , Bean Huo =?utf-8?B?6ZyN5paM5paMLA==?= , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 6/7] mtd: spi-nor: simplify write loop Message-ID: <20151119231857.GM64635@google.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michal, Sorry this has sat so long... On Fri, Aug 14, 2015 at 09:23:08AM -0000, Michal Suchanek wrote: > The spi-nor write loop assumes that what is passed to the hardware > driver write() is what gets written. > > When write() writes less than page size at once data is dropped on the > floor. Check the amount of data writen. Have you seen write() return less than the page size? I know you've struggled with a SPI driver that can't do "very" (for some definition of very) long transfers, due to unknown bugs, but I thought that "very" was much larger than the page size. > This also means that write can start mid-page any time so there is > no special case for first page. I think we'd have some problems if we start seeing hardware that can't write ~256 bytes at a time. If nothing else, this can be a problem because some SPI NOR flash are known to have inferior reliability if you regularly write in small chunks. I believe this is because they actually use some kind of internal ECC. So, if you're just guarding against a theoretical behavior, perhaps it's best if this is done with some kind of assertion, as I'd rather not encourage non-aligned writes if possible. I notice you used BUG_ON() in another patch, but I'd suggest maybe something less harsh, like WARN() or WARN_ONCE(). Brian > > Signed-off-by: Michal Suchanek > --- > drivers/mtd/spi-nor/spi-nor.c | 48 ++++++++++++++----------------------------- > 1 file changed, 15 insertions(+), 33 deletions(-) > > diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c > index 837e3df..e0ae9cf 100644 > --- a/drivers/mtd/spi-nor/spi-nor.c > +++ b/drivers/mtd/spi-nor/spi-nor.c > @@ -836,7 +836,7 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t to, size_t len, > size_t *retlen, const u_char *buf) > { > struct spi_nor *nor = mtd_to_spi_nor(mtd); > - u32 page_offset, page_size, i; > + size_t page_offset, page_remain, i; > int ret; > > dev_dbg(nor->dev, "to 0x%08x, len %zd\n", (u32)to, len); > @@ -845,45 +845,27 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t to, size_t len, > if (ret) > return ret; > > - write_enable(nor); > - > - page_offset = to & (nor->page_size - 1); > + for (i = 0; i < len; ) { > + int written; > > - /* do all the bytes fit onto one page? */ > - if (page_offset + len <= nor->page_size) { > - ret = nor->write(nor, to, len, buf); > - if (ret < 0) > - goto write_err; > - *retlen += ret; > - } else { > + page_offset = to & (nor->page_size - 1); > /* the size of data remaining on the first page */ > - page_size = nor->page_size - page_offset; > - ret = nor->write(nor, to, page_size, buf); > + page_remain = min_t(size_t, > + nor->page_size - page_offset, len - i); > + > + write_enable(nor); > + ret = nor->write(nor, to + i, page_remain, buf + i); > if (ret < 0) > goto write_err; > - *retlen += ret; > - > - /* write everything in nor->page_size chunks */ > - for (i = ret; i < len; ) { > - page_size = len - i; > - if (page_size > nor->page_size) > - page_size = nor->page_size; > - > - ret = spi_nor_wait_till_ready(nor); > - if (ret) > - goto write_err; > + written = ret; > > - write_enable(nor); > - > - ret = nor->write(nor, to + i, page_size, buf + i); > - if (ret < 0) > - goto write_err; > - *retlen += ret; > - i += ret; > - } > + ret = spi_nor_wait_till_ready(nor); > + if (ret) > + goto write_err; > + *retlen += written; > + i += written; > } > > - ret = spi_nor_wait_till_ready(nor); > write_err: > spi_nor_unlock_and_unprep(nor, SPI_NOR_OPS_WRITE); > return ret; > -- > 2.1.4 >