From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BECCC4321E for ; Thu, 5 May 2022 19:53:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1385447AbiEET5f (ORCPT ); Thu, 5 May 2022 15:57:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345160AbiEET53 (ORCPT ); Thu, 5 May 2022 15:57:29 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B2F715F246; Thu, 5 May 2022 12:53:48 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 1BBBFCE3070; Thu, 5 May 2022 19:53:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C68AFC385A4; Thu, 5 May 2022 19:53:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1651780425; bh=fYxm3dr57owbquhz9mi2JlUgAayGWIYeuWXgYwjDgu0=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=f2fc5oHeuzoxyJfE63Gjq/EPrO6txRg9hsHH/1s9bcAA7MB9R89IPW2XirzVZc74o JfbdqHGn2i9se2injqakFs9sJs55qbPwsXCW7U2z6292nsC5wpjZYOXUad+0rDxqWU dBktPS+QUeX5KA0qTdRvD/Jeg8g/VinXCSA1zNxox/sHlz0Qu+HDVGZRGj50as/vwO ee4WTtCWIAPTOcKicttAnfNz1to9P/EIAiFFNcHwyePB8PVEBnOd6hroIfxl+9c3Y0 w8Ysllpp8ZwOIQgubSRRm20/01Cu9xOLyCR6eQMh+KyVf58T4+rzmnxImHp1ouw8wP UdmeA6sO/pypA== Date: Thu, 5 May 2022 14:53:42 -0500 From: Bjorn Helgaas To: Arnd Bergmann Cc: Niklas Schnelle , Arnd Bergmann , Greg Kroah-Hartman , Linux Kernel Mailing List , linux-arch , linux-pci , Richard Henderson , Ivan Kokshaysky , Matt Turner , Russell King , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Michal Simek , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Michael Ellerman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Yoshinori Sato , Rich Felker , "David S. Miller" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "open list:ALPHA PORT" , "moderated list:ARM PORT" , "open list:IA64 (Itanium) PLATFORM" , "open list:M68K ARCHITECTURE" , "open list:MIPS" , "open list:PARISC ARCHITECTURE" , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" , "open list:RISC-V ARCHITECTURE" , "open list:SUPERH" , "open list:SPARC + UltraSPARC (sparc/sparc64)" Subject: Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary Message-ID: <20220505195342.GA509942@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, May 05, 2022 at 07:39:42PM +0200, Arnd Bergmann wrote: > On Thu, May 5, 2022 at 6:10 PM Bjorn Helgaas wrote: > > On Wed, May 04, 2022 at 11:31:28PM +0200, Arnd Bergmann wrote: > > > > > > The main goal is to avoid c), which is what happens on s390, but > > > can also happen elsewhere. Catching b) would be nice as well, > > > but is much harder to do from generic code as you'd need an > > > architecture specific inline asm statement to insert a ex_table > > > fixup, or a runtime conditional on each access. > > > > Or s390 could implement its own inb(). > > > > I'm hearing that generic powerpc kernels have to run both on machines > > that have I/O port space and those that don't. That makes me think > > s390 could do something similar. > > No, this is actually the current situation, and it makes absolutely no > sense. s390 has no way of implementing inb()/outb() because there > are no instructions for it and it cannot tunnel them through a virtual > address mapping like on most of the other architectures. (it has special > instructions for accessing memory space, which is not the same as > a pointer dereference here). > > The existing implementation gets flagged as a NULL pointer dereference > by a compiler warning because it effectively is. I think s390 currently uses the inb() in asm-generic/io.h, i.e., "__raw_readb(PCI_IOBASE + addr)". I understand that's a NULL pointer dereference because the default PCI_IOBASE is 0. I mooted a s390 inb() implementation like "return ~0" because that's what happens on most arches when there's no device to respond to the inb(). The HAS_IOPORT dependencies are fairly ugly IMHO, and they clutter drivers that use I/O ports in some cases but not others. But maybe it's the most practical way. Bjorn