From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from aeryn.fluff.org.uk ([87.194.8.8] helo=kira.home.fluff.org) by bombadil.infradead.org with esmtps (Exim 4.68 #1 (Red Hat Linux)) id 1KwFsO-0004lY-S2 for linux-mtd@lists.infradead.org; Sat, 01 Nov 2008 12:46:49 +0000 Date: Sat, 1 Nov 2008 12:46:34 +0000 From: Ben Dooks To: Werner Almesberger Subject: Re: [PATCH] nand_read_subpage vs. S3C244x NAND: non-word reads Message-ID: <20081101124634.GB11063@fluff.org.uk> References: <20081101031505.GA5177@almesberger.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081101031505.GA5177@almesberger.net> Cc: linux-mtd@lists.infradead.org, Ben Dooks List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, Nov 01, 2008 at 01:15:05AM -0200, Werner Almesberger wrote: > In recent kernels, the optimized OOB reads in nand_read_subpage often > make requests which aren't an exact multiple of a word, which caused > nand/s3c2410.c to do a partial read, yielding chaos and mayhem. > > I'm not entirely sure whether nand_read_subpage is to blame for making > non-word requests, or whether nand/s3c2410.c is to blame for not > supporting them, but here's a patch for the latter. As noted on the openmoko list, I think we can do 256byte subpage reads as long as they are aligned to 256bytes. We could make the ECC code deal with non-256 byte power-of-two aligned blocks without huge changes but my belief is that we cannot support anything that isn't a power of two. I think the best thing to do is to either force the caller to read a power of two (pref. >4 bytes), so either we need some form of flag to say this, or change the behaviour of the callers to never try this. > Note that s3c2410_nand_write_buf has a similar issue. RNDIN is used in > nand_write_oob_syndrome, so this may also be a real problems. > > - Werner > > ---------------------------------- cut here ----------------------------------- > > fix-s3c-nand-read-bytes.patch > > With the introduction of optimized OOB reads in nand_read_subpage, > the length of the data requested may not be a multiple of four bytes. > > This caused a partial read on the 2440, leading to false ECC errors > and, worse, attempts to "correct" them. > > Note that there is a similar issue in s3c2440_nand_write_buf, which > doesn't seem to cause trouble yet. > > Signed-off-by: Werner Almesberger > > --- > > Index: ktrack/drivers/mtd/nand/s3c2410.c > =================================================================== > --- ktrack.orig/drivers/mtd/nand/s3c2410.c 2008-11-01 00:29:45.000000000 -0200 > +++ ktrack/drivers/mtd/nand/s3c2410.c 2008-11-01 00:38:10.000000000 -0200 > @@ -530,7 +530,14 @@ > static void s3c2440_nand_read_buf(struct mtd_info *mtd, u_char *buf, int len) > { > struct s3c2410_nand_info *info = s3c2410_nand_mtd_toinfo(mtd); > + > readsl(info->regs + S3C2440_NFDATA, buf, len / 4); > + if (unlikely(len & 3)) { > + u32 data; > + > + data = readl(info->regs + S3C2440_NFDATA); > + memcpy(buf + (len & ~3), &data, len & 3); > + } note you'll still fail for len in the 0..3 region, as you'll move len+4 bytes, and then copy them over the data you just read. > } > > static void s3c2410_nand_write_buf(struct mtd_info *mtd, const u_char *buf, int len) > > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/ -- Ben (ben@fluff.org, http://www.fluff.org/) 'a smiley only costs 4 bytes'