From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pd0-x22f.google.com ([2607:f8b0:400e:c02::22f]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1YmsNy-0001tz-Ha for linux-mtd@lists.infradead.org; Mon, 27 Apr 2015 23:24:23 +0000 Received: by pdbqa5 with SMTP id qa5so144034605pdb.1 for ; Mon, 27 Apr 2015 16:24:01 -0700 (PDT) Date: Mon, 27 Apr 2015 16:23:53 -0700 From: Brian Norris To: Richard Weinberger Subject: Re: [PATCH 1/3] mtd: nand: Add on-die ECC support Message-ID: <20150427232353.GD32500@ld-irv-0074> References: <1427292151-3835-1-git-send-email-richard@nod.at> <1427292151-3835-2-git-send-email-richard@nod.at> <20150427213558.GA22780@bshelton-desktop> <553EB5E4.3050309@nod.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <553EB5E4.3050309@nod.at> Cc: Boris Brezillon , Ben Shelton , linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, punnaiah.choudary.kalluri@xilinx.com, dwmw2@infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Apr 28, 2015 at 12:19:16AM +0200, Richard Weinberger wrote: > Am 27.04.2015 um 23:35 schrieb Ben Shelton: > > I tested this against the latest version of the PL353 NAND driver that Punnaiah > > has been working to upstream (copying her on this message). With a few changes > > to that driver, I got it most of the way through initialization with on-die ECC > > enabled, but it segfaults here with a null pointer dereference because the > > PL353 driver does not implement chip->cmd_ctrl. Instead, it implements a > > custom override of cmd->cmdfunc that does not call cmd_ctrl. Looking through > > the other in-tree NAND drivers, it looks like most of them do implement > > cmd_ctrl, but quite a few of them do not (e.g. au1550nd, denali, docg4). > > > > What do you think would be the best way to handle this? It seems like this gap > > could be bridged from either side -- either the PL353 driver could implement > > cmd_ctrl, at least as a stub version that provides the expected behavior in > > this case; or the on-die framework could break this out into a callback > > function with a default implementation that the driver could override to > > perform this behavior in the manner of its choosing. > > Oh, I thought every driver has to implement that function. ;-\ Nope. > But you're right there is a corner case. And it's not the only one! Right now, there's no guarantee even that read_buf() returns raw data, unmodified by the SoC's controller. Plenty of drivers actually have HW-enabled ECC turned on by default, and so they override the chip->ecc.read_page() (and sometimes chip->ecc.read_page_raw() functions, if we're lucky) with something that pokes the appropriate hardware instead. I expect anything comprehensive here is probably going to have to utilize chip->ecc.read_page_raw(), at least if it's provided by the hardware driver. > What we could do is just using chip->cmdfunc() with a custom NAND command. > i.e. chip->cmdfunc(mtd, NAND_CMD_READMODE, -1, -1); > > Gerhard Sittig tried to introduce such a command some time ago: > http://lists.infradead.org/pipermail/linux-mtd/2014-April/053115.html Yikes! Please no! It's bad enough to have a ton of drivers doing switch/case on a bunch of real, somewhat well-known opcodes, but to add new fake ones? I'd rather not. We're inflicting ourselves with a kernel-internal version of ioctl(). What's the justification, again? I don't really remember the context of Gerhard's previous patch. Brian