Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030280AbVJER2I (ORCPT ); Wed, 5 Oct 2005 13:28:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030281AbVJER2H (ORCPT ); Wed, 5 Oct 2005 13:28:07 -0400 Received: from ylpvm15-ext.prodigy.net ([207.115.57.46]:9197 "EHLO ylpvm15.prodigy.net") by vger.kernel.org with ESMTP id S1030280AbVJER2G (ORCPT ); Wed, 5 Oct 2005 13:28:06 -0400 X-ORBL: [69.107.75.50] DomainKey-Signature: a=rsa-sha1; s=sbc01; d=pacbell.net; c=nofws; q=dns; h=received:date:from:to:subject:cc:references:in-reply-to: mime-version:content-type:content-transfer-encoding:message-id; b=BLEv19tc/PRixx555rrNHLIfKl41JX1TbAIizqJPdjqY9awOhFu1bk6O5PAPzDdxh f3AGf79DYFBYRpNoAwkSA== Date: Wed, 05 Oct 2005 10:27:49 -0700 From: David Brownell To: rmk+lkml@arm.linux.org.uk Subject: Re: [PATCH/RFC 0/2] simple SPI framework, refresh + ads7864 driver Cc: vwool@ru.mvista.com, linux-kernel@vger.kernel.org References: <20051005162117.24DDBEE95B@adsl-69-107-32-110.dsl.pltn13.pacbell.net> <20051005162453.GD7761@flint.arm.linux.org.uk> In-Reply-To: <20051005162453.GD7761@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20051005172749.C0BE9EE973@adsl-69-107-32-110.dsl.pltn13.pacbell.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2272 Lines: 56 > Date: Wed, 5 Oct 2005 17:24:53 +0100 > From: Russell King > > On Wed, Oct 05, 2005 at 09:21:17AM -0700, David Brownell wrote: > > In my investigations of SPI, I don't happen to have come across any > > SPI slave device that would naturally be handled as a block device. > > There's lots of flash (and dataflash); that's MTD, not block. > > In two words, MMC cards. With the interesting subcase of DataFlash cards, which are MMC format but which only talk SPI protocol. Dataflash would go through MTD. (Seems to me that DataFlash cards are now "old tech" not being put into many new systems. Certainly they're not price-competitive with MMC/SD ... DigiKey charges $US 28 for an 8 MB card, quantity one, and that's the local price of a single 256 MB MMC or SD card. The story with discrete DataFlash chips seems to be different.) > They can be used in MMC mode or SPI mode. Yes, but ... any system with an MMC controller would use them in MMC mode; then they'd be "MMC devices". (Except DataFlash...) The reason to use them in SPI mode is that that the system might not _have_ an MMC controller, yet it might want inexpensive removable storage. (And there's another funky case too. Most MMC controllers will handle SPI protocol directly; I'm not sure how full the support is, maybe it's just enough to talk to MMC cards. But systems that want SPI -- say, for sensors -- might do that using their MMC controllers on one of the chipselects that's not used for an external card slot.) > There have been some queries > about using them in SPI mode, but I don't think anyone's written such > a driver (yet). Nor does the MMC stack yet understand that notion... it'd likely help a bit if there were an SPI framework to build on! Teaching that stack how to work in SPI mode, or even represent controllers which only support SPI protocol, would be a lot more work than just letting SPI drivers optionally provide DMA addresses as well as the CPU addresses for their buffers. :) - Dave - 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/