From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Brezillon Subject: Re: [PATCH] mtd: rawnand: denali: add DT property to specify skipped bytes in OOB Date: Fri, 7 Sep 2018 16:08:22 +0200 Message-ID: <20180907160822.319047c8@bbrezillon> References: <1536317783-4942-1-git-send-email-yamada.masahiro@socionext.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1536317783-4942-1-git-send-email-yamada.masahiro@socionext.com> Sender: linux-kernel-owner@vger.kernel.org To: Masahiro Yamada Cc: linux-mtd@lists.infradead.org, Miquel Raynal , devicetree@vger.kernel.org, Rob Herring , Dinh Nguyen , linux-kernel@vger.kernel.org, Marek Vasut , Brian Norris , Richard Weinberger , David Woodhouse , Mark Rutland List-Id: devicetree@vger.kernel.org Hi Masahiro, On Fri, 7 Sep 2018 19:56:23 +0900 Masahiro Yamada wrote: > NAND devices need additional data area (OOB) for error correction, > but it is also used for Bad Block Marker (BBM). In many cases, the > first byte in OOB is used for BBM, but the location actually depends > on chip vendors. The NAND controller should preserve the precious > BBM to keep track of bad blocks. > > In Denali IP, the SPARE_AREA_SKIP_BYTES register is used to specify > the number of bytes to skip from the start of OOB. The ECC engine > will automatically skip the specified number of bytes when it gets > access to OOB area. > > The same value for SPARE_AREA_SKIP_BYTES should be used between > firmware and the operating system if you intend to use the NAND > device across the control hand-off. > > In fact, the current denali.c code expects firmware to have already > set the SPARE_AREA_SKIP_BYTES register, then reads the value out. > > If no firmware (or bootloader) has initialized the controller, the > register value is zero, which is the default after power-on-reset. > > In other words, the Linux driver cannot initialize the controller > by itself. You cannot support the reset control either because > resetting the controller will get register values lost. > > This commit adds a way to specify it via DT. If the property > "denali,oob-skip-bytes" exists, the value will be set to the register. Hm, do we really need to make this config customizable? I mean, either you have a large-page NAND (page > 512 bytes) and the 2 first bytes must be reserved for the BBM or you have a small-page NAND and the BBM is at position 4 and 5. Are you sure people configure that differently? Don't you always have SPARE_AREA_SKIP_BYTES set to 6 or 2? Regards, Boris