Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932297AbbD1CsR (ORCPT ); Mon, 27 Apr 2015 22:48:17 -0400 Received: from mail-pd0-f178.google.com ([209.85.192.178]:34454 "EHLO mail-pd0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932251AbbD1CsM (ORCPT ); Mon, 27 Apr 2015 22:48:12 -0400 MIME-Version: 1.0 In-Reply-To: <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> <20150427232353.GD32500@ld-irv-0074> Date: Tue, 28 Apr 2015 08:18:12 +0530 X-Google-Sender-Auth: mSfTxYixKQkYRxsY2H5pF8eOWsc Message-ID: Subject: Re: [PATCH 1/3] mtd: nand: Add on-die ECC support From: punnaiah choudary kalluri To: Brian Norris Cc: Richard Weinberger , Ben Shelton , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" , David Woodhouse , Punnaiah Choudary Kalluri , Boris Brezillon Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3388 Lines: 69 On Tue, Apr 28, 2015 at 4:53 AM, Brian Norris wrote: > 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. Yes, overriding the chip->ecc.read_page_raw would solve this. Agree that read_buf need not be returning raw data always including my new driver for arasan nand flash controller. http://lkml.iu.edu/hypermail/linux/kernel/1504.2/00313.html Regards, Punnaiah > >> 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 > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/