Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751186AbdFAUrR convert rfc822-to-8bit (ORCPT ); Thu, 1 Jun 2017 16:47:17 -0400 Received: from mail.free-electrons.com ([62.4.15.54]:51213 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751024AbdFAUrP (ORCPT ); Thu, 1 Jun 2017 16:47:15 -0400 Date: Thu, 1 Jun 2017 22:47:12 +0200 From: Boris Brezillon To: Brian Norris Cc: Chris Packham , dwmw2@infradead.org, andrew@lunn.ch, linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org, Marek Vasut , Richard Weinberger , Cyrille Pitchen Subject: Re: [PATCH 3/4] mtd: mchp23k256: add partitioning support Message-ID: <20170601224712.6a81a458@bbrezillon> In-Reply-To: <20170601184340.GA102137@google.com> References: <20170517053908.26138-1-chris.packham@alliedtelesis.co.nz> <20170517053908.26138-4-chris.packham@alliedtelesis.co.nz> <20170517172911.5f926712@bbrezillon> <20170601184340.GA102137@google.com> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2881 Lines: 71 Le Thu, 1 Jun 2017 11:43:40 -0700, Brian Norris a écrit : > On Wed, May 17, 2017 at 05:29:11PM +0200, Boris Brezillon wrote: > > Hi Chris, > > > > On Wed, 17 May 2017 17:39:07 +1200 > > Chris Packham wrote: > > > > > Setting the of_node for the mtd device allows the generic mtd code to > > > setup the partitions. Additionally we must specify a non-zero erasesize > > > for the partitions to be writeable. > > > > > > Signed-off-by: Chris Packham > > > --- > > > drivers/mtd/devices/mchp23k256.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/drivers/mtd/devices/mchp23k256.c b/drivers/mtd/devices/mchp23k256.c > > > index 2542f5b8b63f..02c6b9dcbd3e 100644 > > > --- a/drivers/mtd/devices/mchp23k256.c > > > +++ b/drivers/mtd/devices/mchp23k256.c > > > @@ -143,6 +143,7 @@ static int mchp23k256_probe(struct spi_device *spi) > > > > > > data = dev_get_platdata(&spi->dev); > > > > > > + mtd_set_of_node(&flash->mtd, spi->dev.of_node); > > > flash->mtd.dev.parent = &spi->dev; > > > flash->mtd.type = MTD_RAM; > > > flash->mtd.flags = MTD_CAP_RAM; > > > @@ -151,6 +152,10 @@ static int mchp23k256_probe(struct spi_device *spi) > > > flash->mtd._read = mchp23k256_read; > > > flash->mtd._write = mchp23k256_write; > > > > > > + flash->mtd.erasesize = PAGE_SIZE; > > > + while (flash->mtd.size & (flash->mtd.erasesize - 1)) > > > + flash->mtd.erasesize >>= 1; > > > + > > > > Can we fix allocate_partition() to properly handle the > > master->erasesize == 0 case instead of doing that? > > Is everything actually ready for the eraseblock size to be 0? That would > seem surprising to many applications, I would think. Can you, for > instance, even use UBI on such a device? Well, I think it's already broken. AFAICT this driver does not implement ->_erase(), and mtd_erase() does not check if MTD_NO_ERASE is set before calling mtd->_erase(), neither UBI does before calling mtd_erase(). Between a NULL pointer exception and a div-by-zero exception, I can't decide what is better :-). IMO, we'd better add a check in UBI to refuse to attach a device with MTD_NO_ERASE or mtd->erasesize == 0, and fix other places that don't check erasesize value instead of putting a fake erasesize and using a dummy ->_erase() implementation for those devices that simply can't be erased. We should also probably complain with -ENOTSUPP when someone calls mtd_erase() on a device with MTD_NO_ERASE and add more checks in the add_mtd_device() to detect drivers that don't have MTD_NO_ERASE set and do not implement ->_erase() or leave ->erasesize to 0. > > BTW, I feel like this check is a little more natural to do with > 'mtd->flags & MTD_NO_ERASE', rather than checking the (apparently > meaningless) erasesize. Fair enough.