Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755007AbZDUI5Y (ORCPT ); Tue, 21 Apr 2009 04:57:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752735AbZDUI5G (ORCPT ); Tue, 21 Apr 2009 04:57:06 -0400 Received: from rv-out-0506.google.com ([209.85.198.235]:32500 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752484AbZDUI5D convert rfc822-to-8bit (ORCPT ); Tue, 21 Apr 2009 04:57:03 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=KquDnWCNkWdkSX8SYr4M8CZwJxp5rG113p3RFhdBn2IKP7ecQ36L6eHxeVIBx5YZQm jeiwk8omHuR7g6MBSY3LRfqgxNpYGOp8+xoBa8zGATRK/MH1wrr0a7+sw3lZVOwT6NRk jOamMcy+hDhpjESMiz2DeLvfoWCpq6WFmy9hI= MIME-Version: 1.0 In-Reply-To: <20090421084521.GA20459@elte.hu> References: <20090419214602.GA21527@elte.hu> <49EBCDC0.1020001@zytor.com> <20090420105304.GC6670@elte.hu> <20090420160332.GB9689@elte.hu> <20090421084521.GA20459@elte.hu> Date: Tue, 21 Apr 2009 17:57:02 +0900 Message-ID: Subject: Re: arch/x86/Kconfig selects invalid HAVE_READQ, HAVE_WRITEQ vars From: Hitoshi Mitake To: Ingo Molnar Cc: "H. Peter Anvin" , Roland Dreier , Thomas Gleixner , "Robert P. J. Day" , Linux Kernel Mailing List Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3426 Lines: 80 On Tue, Apr 21, 2009 at 17:45, Ingo Molnar wrote: > > * Hitoshi Mitake wrote: > >> On Tue, Apr 21, 2009 at 01:03, Ingo Molnar wrote: >> > >> > * Hitoshi Mitake wrote: >> > >> >> On Mon, Apr 20, 2009 at 19:53, Ingo Molnar wrote: >> >> > >> >> > * H. Peter Anvin wrote: >> >> > >> >> >> Roland Dreier wrote: >> >> >> > >> >> >> > Notice that it reads from addr+4 *before* it reads from addr, rather >> >> >> > than after as in your example (and in fact your example depends on >> >> >> > undefined compiler semantics, since there is no sequence point between >> >> >> > the two operands of the | operator). ?Now, I don't know that hardware, >> >> >> > so I don't know if it makes a difference, but the niu example I gave in >> >> >> > my original email shows that given hardware with clear-on-read >> >> >> > registers, the order does very much matter. >> >> >> > >> >> >> >> >> >> At least for x86, the order should be low-high, because that is the >> >> >> order that those two transactions would be seen on a 32-bit bus >> >> >> downstream from the CPU if the CPU issued a 64-bit transaction. >> >> >> >> >> >> The only sane way to handle this as something other than per-driver >> >> >> hacks would be something like: >> >> >> >> >> >> #include ? ? ? ? ? ? ? /* Any 64-bit I/O OK */ >> >> >> >> >> >> #include ? ? /* Low-high splitting OK */ >> >> >> >> >> >> #include ? ? /* High-low splitting OK */ >> >> >> >> >> >> #include /* 64-bit I/O must be atomic */ >> >> >> >> >> >> ... i.e. letting the driver choose what fallback method it will accept. >> >> > >> >> > Yeah - with the default being the natural low-high order. >> >> > >> >> > The other argument is that if a driver really wants some rare, oddly >> >> > different order it should better define its own method that is not >> >> > named in the same (or in a similar) way as an existing generic API. >> >> > Otherwise, confusion will ensue. >> >> I think this is a good way. >> >> readq/writeq are already in Linus's tree, removing these is not a good idea. >> >> >> >> And I've sent the patch to fix a little problem of Kconfig about >> >> readq/writeq to you. >> >> http://marc.info/?l=linux-kernel&m=123521109218008&w=2 >> >> Did you notice? >> >> >> >> Adding cautions about accessing order or non-atomic to Kconfig's help >> >> part may be benefit. >> > >> > It's better to add add such non-interactive help text as Makefile >> > comments: >> > >> > # >> > # This option ... >> > # >> > >> > and they should be invisible in make menuconfig. This is a facility >> > provided by architectures. >> I'll move the help text from Kconfig to Makefile. >> (My original patch also doesn't make help text visible in make menuconfig.) > > sorry i meant the Kconfig file - you can put comments in there too. > help text is really meant for things that are interactive. Can I think that I should add help text to both of Kconfig and Makefile? (I'm not a native English speaker, and I'm not good at English. I'm sorry if I misunderstand something...) -- 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/