From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ezequiel Garcia Subject: Re: [PATCH v5 1/3] mtd: nand: gpio: Add DT property to automatically determine bus width Date: Sat, 30 Nov 2013 08:17:22 -0300 Message-ID: <20131130111721.GA2330@localhost> References: <1384343884-29622-1-git-send-email-shc_work@mail.ru> <20131127012158.GR9468@ld-irv-0074.broadcom.com> <20131127012338.GS9468@ld-irv-0074.broadcom.com> <20131129122551.GC2815@localhost> <20131130091556.GD29397@norris.computersforpeace.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20131130091556.GD29397-7ciq9WCbhwJWVhifINYOO1poFGfAdsVx5NbjCUgZEJk@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Brian Norris Cc: Alexander Shiyan , linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Mark Rutland , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Ian Campbell , Russell King , Pawel Moll , Artem Bityutskiy , Stephen Warren , Rob Herring , Haojian Zhuang , Eric Miao , David Woodhouse , Pekon Gupta List-Id: devicetree@vger.kernel.org Brian, On Sat, Nov 30, 2013 at 01:15:56AM -0800, Brian Norris wrote: >=20 > > Can anyone help me understand if there's *any* valid use case where= we > > want to specify a-priori the bus width, considering it's completely > > discoverable at run-time? >=20 > I think the primary use case should be to reflect a limitation in the > hardware (besides just the flash chip). It can mean that the controll= er > itself only supports one bus width, or that the board is only wired u= p > for x8, for instance. >=20 What do you mean by "reflect a limitation" of the hardware? Maybe I'm not really following you, but it sounds as you're mixing up the NAND device buswidth and the memory controller buswidth. At least I consider them as two different parameters for two different pieces of hardware. Consider OMAP, just as an example. We currently have two DT properties: 1. nand-bus-width: not related to OMAP but kernel wide. It's supposed to specify the devices buswidth. 2. gpmc,device-width: It specifies how the controller should be configured (it doesn't really specify hardware, but configuration, sadly). I now realise maybe this piece of DT binding is not a good example of D= T. Anyway, once again: Why would we need to set "nand-bus-width" to specif= y the flash device width given we can discover that as soon as the NAND is detected? Notice, that this discussion is independent of the discussion about rem= oving the NAND_BUSWIDTH_AUTO. It's just about removing a DT property for a parameter that's runtime configurable. --=20 Ezequiel Garc=C3=ADa, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html