From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 04 May 2012 03:18:15 +0200 (CEST) Received: from mail-pb0-f49.google.com ([209.85.160.49]:64253 "EHLO mail-pb0-f49.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S1903771Ab2EDBSI (ORCPT ); Fri, 4 May 2012 03:18:08 +0200 Received: by pbbrq13 with SMTP id rq13so3428443pbb.36 for ; Thu, 03 May 2012 18:18:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=l4sAEpx8MjtX1KI7Lhv/D/Am3O/SilbAfdb4moW3Uko=; b=H/8yAbyfwkQj0JVsdNbDGzpAgV005Sxg3Ry1nCViXQzGuC85XIvW+4MZcuAxDFAJVj KCP6poyWYlQNvVYz5VaGHlB7KybhchPgwN2Il3EimgtUPnEzOjRzJRLoH+SOcJ/2+p1+ kSycSLIXxhV6cCiKNLq+rqyhSVdLmhGPW6u6c0WA9vc+M6EasioEe5z/4i0BOtZN+471 myrkHP/4Leuo1B6Mp+k8wdgH5okw5RKuHrUi5nnzO55aI4ugPAHU869xYQ5bGKgeLYjh YUCw9EwON05xpRWBUOBGlgfqOMuO0ZbRLtvJN/8fKxTJXyZGVF2aE8A8xDNkLh5VRyQz 2Jlw== Received: by 10.68.200.74 with SMTP id jq10mr1839952pbc.66.1336094282010; Thu, 03 May 2012 18:18:02 -0700 (PDT) Received: from dd1.caveonetworks.com (64.2.3.195.ptr.us.xo.net. [64.2.3.195]) by mx.google.com with ESMTPS id ky10sm117171pbc.0.2012.05.03.18.18.00 (version=SSLv3 cipher=OTHER); Thu, 03 May 2012 18:18:00 -0700 (PDT) Message-ID: <4FA32E47.7020406@gmail.com> Date: Thu, 03 May 2012 18:17:59 -0700 From: David Daney User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 MIME-Version: 1.0 To: Bjorn Helgaas CC: John Crispin , Ralf Baechle , Grant Likely , linux-pci@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, linux-mips@linux-mips.org Subject: Re: [PATCH] OF: PCI: const usage needed by MIPS References: <1335808019-24502-1-git-send-email-blogic@openwrt.org> <4F9ED1DC.3050007@gmail.com> <4F9FE4F6.5070909@openwrt.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-archive-position: 33136 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ddaney.cavm@gmail.com Precedence: bulk X-list: linux-mips Return-Path: On 05/03/2012 05:30 PM, Bjorn Helgaas wrote: > On Tue, May 1, 2012 at 7:28 AM, John Crispin wrote: >> On 30/04/12 19:54, David Daney wrote: >>> On 04/30/2012 10:46 AM, John Crispin wrote: >>>> On MIPS we want to call of_irq_map_pci from inside >>>> >>>> arch/mips/include/asm/pci.h:extern int pcibios_map_irq( >>>> const struct pci_dev *dev, u8 slot, u8 pin); >>>> >>>> For this to work we need to change several functions to const usage. >>> >>> I think there is a mismatch on this throughout the kernel. >>> >>> Properly fixing it requires touching many more places than these. >>> Although I haven't tried it, I wouldn't be surprised if doing this >>> caused warnings to appear in non-MIPS code. >>> >>> Ralf had a patch at one point that tried to make this consistent >>> tree-wide, but it is not yet applied. >>> >>> David Daney >> >> Hi, >> >> Ok, lets see what Ralf has to say. >> >> I just tested the patch on x86 with OF enabled and drivers turned on >> that use the API. I did not see any errors appear. > > I'm far from a const expert, but I think this should be safe. > Here's my reasoning: > > We're changing pci_swizzle_interrupt_pin() to take a pointer to a > constant struct pci_dev. pci_swizzle_interrupt_pin() only reads the > struct pci_dev; it doesn't modify it. It is legal to pass either > "struct pci_dev *" or "const struct pci_dev *" to a function expecting > "const struct pci_dev *"; the callee just won't be able to modify the > struct, even if the caller can. > The problem is when you start declaring function pointers in various ops vectors. Consider: void (*foo)(const struct pci_dev *) void (*bar)(struct pci_dev *) foo and bar are not type compatible, and you will get compiler warnings if you use one where the other is expected. So the question is: Are we ever going to the address of any of the functions that are being modified? If so, we have created a problem. > Similar reasoning applies to of_irq_map_pci(). > > So I'm fine with this. You sent it to Grant, so I'll assume he'll > merge it unless I hear otherwise. > > Acked-by: Bjorn Helgaas >