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 34EC2C433F5 for ; Fri, 6 May 2022 13:28:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1392548AbiEFNcd convert rfc822-to-8bit (ORCPT ); Fri, 6 May 2022 09:32:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59662 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1392534AbiEFNcb (ORCPT ); Fri, 6 May 2022 09:32:31 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 252F4167ED for ; Fri, 6 May 2022 06:28:46 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-216-O2D6viKlNf-4TslEv6Mr8Q-1; Fri, 06 May 2022 14:28:44 +0100 X-MC-Unique: O2D6viKlNf-4TslEv6Mr8Q-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Fri, 6 May 2022 14:28:42 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Fri, 6 May 2022 14:28:42 +0100 From: David Laight To: "'Maciej W. Rozycki'" CC: Arnd Bergmann , Rich Felker , "open list:IA64 (Itanium) PLATFORM" , "open list:SUPERH" , Catalin Marinas , Dave Hansen , "open list:MIPS" , "James E.J. Bottomley" , "open list:SPARC + UltraSPARC (sparc/sparc64)" , "open list:RISC-V ARCHITECTURE" , Will Deacon , linux-arch , Yoshinori Sato , Helge Deller , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Russell King , Ingo Molnar , Geert Uytterhoeven , linux-pci , Bjorn Helgaas , Matt Turner , Albert Ou , Arnd Bergmann , Niklas Schnelle , "open list:M68K ARCHITECTURE" , Ivan Kokshaysky , Paul Walmsley , "Thomas Gleixner" , "moderated list:ARM PORT" , Richard Henderson , Michal Simek , Thomas Bogendoerfer , "open list:PARISC ARCHITECTURE" , Greg Kroah-Hartman , Linux Kernel Mailing List , Palmer Dabbelt , "open list:ALPHA PORT" , Borislav Petkov , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" , "David S. Miller" Subject: RE: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary Thread-Topic: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary Thread-Index: AQHYYUSwX3QwDKjE7kKG/gGNt1cnA60Rx6Pg///7pACAABHIsA== Date: Fri, 6 May 2022 13:28:42 +0000 Message-ID: <3669a28a055344a792b51439c953fd30@AcuMS.aculab.com> References: <20220505161028.GA492600@bhelgaas> <5239892986c94239a122ab2f7a18a7a5@AcuMS.aculab.com> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org From: Maciej W. Rozycki > Sent: 06 May 2022 14:15 > On Fri, 6 May 2022, David Laight wrote: > > > > The PCI configuration space was retrofitted into x86 systems (and is > > > accessed in an awkward manner with them), but with a new design such a > > > clean approach is most welcome IMHO. Thank you for your explanation. > > > > Actually I think x86 was the initial system for PCI. > > The PCI config space 'mess' is all about trying to make > > something that wouldn't break existing memory maps. > > It was retrofitted in that x86 systems already existed for ~15 years when > PCI came into picture. Therefore the makers of the CPU ISA couldn't have > envisaged the need for config access instructions like they did for memory > and port access. Rev 2.0 of the PCI spec (1993) defines two mechanisms for config cycles. #2 is probably the first one and maps all of PCI config space into 4k of IO space (PCI bridges aren't supported). #1 requires a pair of accesses (and SMP locking). Neither is really horrid. For horrid try the ISApnp interface. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)