Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754799AbYFEOnY (ORCPT ); Thu, 5 Jun 2008 10:43:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752916AbYFEOnO (ORCPT ); Thu, 5 Jun 2008 10:43:14 -0400 Received: from rtsoft3.corbina.net ([85.21.88.6]:24135 "EHLO buildserver.ru.mvista.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752035AbYFEOnN (ORCPT ); Thu, 5 Jun 2008 10:43:13 -0400 Date: Thu, 5 Jun 2008 18:43:10 +0400 From: Anton Vorontsov To: Marc Pignat Cc: Kumar Gala , David Brownell , Pierre Ossman , Jochen Friedrich , Timur Tabi , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, spi-devel-general@lists.sourceforge.net Subject: Re: [PATCH 3/3] mmc: change .get_ro() callback semantics Message-ID: <20080605144310.GA31596@polina.dev.rtsoft.ru> Reply-To: avorontsov@ru.mvista.com References: <20080523154204.GA19803@polina.dev.rtsoft.ru> <20080523154347.GC24862@polina.dev.rtsoft.ru> <200806031207.49843.marc.pignat@hevs.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Disposition: inline In-Reply-To: <200806031207.49843.marc.pignat@hevs.ch> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2216 Lines: 54 On Tue, Jun 03, 2008 at 12:07:49PM +0200, Marc Pignat wrote: > Hi all! > > On Friday 23 May 2008, Anton Vorontsov wrote: > > get_ro() callback must return values >= 0 for its logical state, and > ... > > static void pxamci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios) > > diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h > > index f2e9885..ef3b773 100644 > > --- a/include/linux/mmc/host.h > > +++ b/include/linux/mmc/host.h > > @@ -55,6 +55,9 @@ struct mmc_host_ops { > > * Avoid calling these three functions too often or in a "fast path", > > * since underlaying controller might implement them in an expensive > > * and/or slow way. > > + * > > + * .get_ro and .get_cd should return >= 0 for their logical values, > > + * or negative errno value in case of error. > > */ > > I would suggest to use something more strict (bulletproof), something like: > > /* > * get_ro will return: > * 0 for a read/write card > * 1 for a read-only card This isn't always practical. For example, host is using u8 register for the status, so it might safely return u8 & mask, that will always fit into int. Or very smart/adventurous authors might be aware that, for the particular host, mask's bit isn't last, and safely do uXX & mask. :-) The above is weak argument of course, since it is about optimization. As an counter-evidence, the strict scheme that you described probably less error prone. But is it? To implement it we'll need something like WARN_ON(ret > 0 && ret != 1) to catch erroneous users. Take a closer look though, will it catch uXX & lastbit case? Nope. :-) We can catch bogus users though... via hack (_assuming_ that there are no errno values of 1 << (sizeof(int) * 8 - 1)), i.e. WARN_ON(ret == (1 << (sizeof(int) * 8 - 1)). Though, to do so, we don't need the strict scheme, this debugging hack will work in the current scheme too. -- Anton Vorontsov email: cbouatmailru@gmail.com irc://irc.freenode.net/bd2 -- 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/