From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Madhusudhan" Subject: RE: [PATCH v3] OMAP: Fix for bus width which improves SD card's peformance. Date: Tue, 6 Apr 2010 19:16:49 -0500 Message-ID: <00c901cad5e7$9de54350$544ff780@am.dhcp.ti.com> References: <003b01cad0f0$6ea78040$544ff780@am.dhcp.ti.com> <003c01cad1b1$da2cdbf0$544ff780@am.dhcp.ti.com> <20100405164839.GB17388@gandalf> <007c01cad4e4$26c5a700$544ff780@am.dhcp.ti.com> <20100406050035.GA32537@gandalf> <003901cad5a4$730264d0$544ff780@am.dhcp.ti.com> <20100406163211.GA29117@nokia.com> <4BBB6767.7010202@ti.com> <20100406165720.GA17916@nokia.com> <00b401cad5e0$1d1868d0$544ff780@am.dhcp.ti.com> <4BBBC628.9030207@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from arroyo.ext.ti.com ([192.94.94.40]:39074 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932227Ab0DGARE (ORCPT ); Tue, 6 Apr 2010 20:17:04 -0400 In-Reply-To: <4BBBC628.9030207@ti.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: 'Nishanth Menon' Cc: felipe.balbi@nokia.com, me@felipebalbi.com, 'kishore kadiyala' , 'Vimal Singh' , tony@atomide.com, "'S, Venkatraman'" , linux-omap@vger.kernel.org, linux-kernel@vger.kernel.org, "'Lavinen Jarkko (Nokia-D/Helsinki)'" > -----Original Message----- > From: Nishanth Menon [mailto:nm@ti.com] > Sent: Tuesday, April 06, 2010 6:39 PM > To: Chikkature Rajashekar, Madhusudhan > Cc: felipe.balbi@nokia.com; me@felipebalbi.com; 'kishore kadiyala'; 'Vimal > Singh'; tony@atomide.com; S, Venkatraman; linux-omap@vger.kernel.org; > linux-kernel@vger.kernel.org; 'Lavinen Jarkko (Nokia-D/Helsinki)' > Subject: Re: [PATCH v3] OMAP: Fix for bus width which improves SD card's > peformance. > > Chikkature Rajashekar, Madhusudhan had written, on 04/06/2010 06:23 PM, > the following: > > > >> -----Original Message----- > >> From: Felipe Balbi [mailto:felipe.balbi@nokia.com] > >> Sent: Tuesday, April 06, 2010 11:57 AM > >> To: ext Nishanth Menon > >> Cc: Balbi Felipe (Nokia-D/Helsinki); Chikkature Rajashekar, > Madhusudhan; > >> me@felipebalbi.com; 'kishore kadiyala'; 'Vimal Singh'; > tony@atomide.com; > >> S, Venkatraman; linux-omap@vger.kernel.org; linux- > kernel@vger.kernel.org; > >> Lavinen Jarkko (Nokia-D/Helsinki) > >> Subject: Re: [PATCH v3] OMAP: Fix for bus width which improves SD > card's > >> peformance. > >> > >> On Tue, Apr 06, 2010 at 06:55:03PM +0200, ext Nishanth Menon wrote: > >>> some reasons why i love switch statements ;) since I dont expect other > >>> than precisely 4 and 8 (do we expect 5,6,7 - i might be wrong).. but > if > >>> it is so, wont the following be better? > >>> > >>> switch (mmc_slot(host).wires) > >>> { > >>> case 8: > >>> mmc->caps |= MMC_CAP_8_BIT_DATA; > >>> /* fall thru*/ > >>> case 4: > >>> mmc->caps |= MMC_CAP_4_BIT_DATA; > >>> break; > >>> default: > >>> WARN("bad width"); > >>> } > >> I like that, but I remember Madhu (or someone else) saying he thinks > >> it's less readable this way. Go figure... > >> > > Well, I did not comment on the usage of switch here. Note we only need > to > > handle 8-bit and 4-bit.The board files need not setup 8-bit or 4-bit if > the > > configuration of that board is 1-bit. The driver will still work in 1- > bit > > mode which would mean there is nothing to do in default case and should > not > > err out. > check the attachment out.. hope that takes care of it.. just as a > reference alone ofcourse.. Nope. The default case is wrong. The assumption followed by controller drivers is that if the board file says 4-bit or 8-bit set the capabilities otherwise don't do any thing. The host will continue to work in 1-bit mode which is a must. Your patch violates that (can not design a board without connecting one data line at least :)) Also you can not say 1-bit is non-optimal because the board file dictates the configuration based on what it is capable of. Why through a warning? It is subjective. Regards, Madhu > -- > Regards, > Nishanth Menon