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 0148AC4167B for ; Fri, 6 May 2022 11:20:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1391276AbiEFLYU (ORCPT ); Fri, 6 May 2022 07:24:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1391303AbiEFLYH (ORCPT ); Fri, 6 May 2022 07:24:07 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BE6D61136; Fri, 6 May 2022 04:20:22 -0700 (PDT) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 246AxYnp014029; Fri, 6 May 2022 11:18:58 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=message-id : subject : from : to : cc : date : in-reply-to : references : content-type : content-transfer-encoding : mime-version; s=pp1; bh=y5OiXKtWxrE9jkRNnZnUPIxSoW5NO888lYPMeY8p20o=; b=KUrZVHNedJMQHXRUcjFYRz49EjLPt/z8Enxpe963RBRHVwRMBIajjKHTbAEmyQygRzWc lvtblkDBEv0KM5s9aGvgB1VbknJOF47xy4utbk/2sTFacNlPn+6id8sHDSEmtYqCHgce bb8f78CA6OZEGHds6XuwyfyNYtjQ/Sz14sYUz2gP0WSwg3pg800hXKb7bnHzDJeiHtFZ dZaiepyf5OYOjy0JX7QcOFu7TIf6eefQLMPf+V2/m05DTHXeyKaCpGjGJHSckMTQJXTK 0SdLpB5S8k05thmQVCh28GCCFzfAXO02Xps+YQB3gva5HPAW0rJhQpu/5Dq/ASHPVitd Ng== Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com (PPS) with ESMTPS id 3fw2dm8asx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 06 May 2022 11:18:58 +0000 Received: from m0098413.ppops.net (m0098413.ppops.net [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 246BI0IY021612; Fri, 6 May 2022 11:18:57 GMT Received: from ppma03ams.nl.ibm.com (62.31.33a9.ip4.static.sl-reverse.com [169.51.49.98]) by mx0b-001b2d01.pphosted.com (PPS) with ESMTPS id 3fw2dm8asf-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 06 May 2022 11:18:57 +0000 Received: from pps.filterd (ppma03ams.nl.ibm.com [127.0.0.1]) by ppma03ams.nl.ibm.com (8.16.1.2/8.16.1.2) with SMTP id 246BHWn0005982; Fri, 6 May 2022 11:18:55 GMT Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by ppma03ams.nl.ibm.com with ESMTP id 3ftp7fwcut-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 06 May 2022 11:18:55 +0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 246BIrKO46924078 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 6 May 2022 11:18:53 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 27ED14C044; Fri, 6 May 2022 11:18:53 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 641CB4C046; Fri, 6 May 2022 11:18:51 +0000 (GMT) Received: from sig-9-145-46-59.uk.ibm.com (unknown [9.145.46.59]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 6 May 2022 11:18:51 +0000 (GMT) Message-ID: <105ccec439f709846e82b69cb854ac825d7a6a49.camel@linux.ibm.com> Subject: Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary From: Niklas Schnelle To: Finn Thain , Bjorn Helgaas Cc: Arnd Bergmann , 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)" Date: Fri, 06 May 2022 13:18:51 +0200 In-Reply-To: <22bec167-241f-2cbe-829f-a3f65e40e71@linux-m68k.org> References: <20220505195342.GA509942@bhelgaas> <22bec167-241f-2cbe-829f-a3f65e40e71@linux-m68k.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-18.el8) X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 5UqqC9GevofRxBeHStbLnLlUH6eZ3euH X-Proofpoint-ORIG-GUID: w_xuM4uo82W1hTrsAd4vNrc6YUx1BE02 Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-06_03,2022-05-06_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 mlxlogscore=999 clxscore=1011 spamscore=0 adultscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 bulkscore=0 suspectscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205060062 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, 2022-05-06 at 19:12 +1000, Finn Thain wrote: > > On Thu, 5 May 2022, Bjorn Helgaas wrote: > > > 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. > > > > Do you mean, "the most practical way to avoid a compiler warning on s390"? > What about "#pragma GCC diagnostic ignored"? This actually happens with clang. Apart from that, I think this would also fall under the same argument as the original patch Linus unpulled. We would just paint over someting that we know at compile time won't work: https://lore.kernel.org/lkml/CAHk-=wg80je=K7madF4e7WrRNp37e3qh6y10Svhdc7O8SZ_-8g@mail.gmail.com/