From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anton Vorontsov Subject: Re: [PATCH 3/3] mmc: change .get_ro() callback semantics Date: Thu, 5 Jun 2008 18:43:10 +0400 Message-ID: <20080605144310.GA31596@polina.dev.rtsoft.ru> References: <20080523154204.GA19803@polina.dev.rtsoft.ru> <20080523154347.GC24862@polina.dev.rtsoft.ru> <200806031207.49843.marc.pignat@hevs.ch> Reply-To: avorontsov@ru.mvista.com Mime-Version: 1.0 Content-Type: text/plain; charset=utf8 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 To: Marc Pignat Return-path: Content-Disposition: inline In-Reply-To: <200806031207.49843.marc.pignat@hevs.ch> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from buildserver.ru.mvista.com (unknown [85.21.88.6]) by ozlabs.org (Postfix) with ESMTP id 755DEDE5C7 for ; Fri, 6 Jun 2008 00:43:13 +1000 (EST) Date: Thu, 5 Jun 2008 18:43:10 +0400 From: Anton Vorontsov To: Marc Pignat Subject: Re: [PATCH 3/3] mmc: change .get_ro() callback semantics Message-ID: <20080605144310.GA31596@polina.dev.rtsoft.ru> 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 In-Reply-To: <200806031207.49843.marc.pignat@hevs.ch> Cc: David Brownell , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, spi-devel-general@lists.sourceforge.net, Timur Tabi , Pierre Ossman Reply-To: avorontsov@ru.mvista.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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