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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1AD1C433ED for ; Fri, 14 May 2021 13:13:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B5D56145E for ; Fri, 14 May 2021 13:13:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232046AbhENNOg convert rfc822-to-8bit (ORCPT ); Fri, 14 May 2021 09:14:36 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]:58425 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbhENNOf (ORCPT ); Fri, 14 May 2021 09:14:35 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-76-GxO-xKM-MNOH8CDoNhHeWQ-1; Fri, 14 May 2021 14:13:21 +0100 X-MC-Unique: GxO-xKM-MNOH8CDoNhHeWQ-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 15.0.1497.2; Fri, 14 May 2021 14:13:19 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.015; Fri, 14 May 2021 14:13:19 +0100 From: David Laight To: 'Thomas Gleixner' , 'Maximilian Luz' , Ingo Molnar , Borislav Petkov CC: "H. Peter Anvin" , Sachi King , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: RE: [PATCH] x86/i8259: Work around buggy legacy PIC Thread-Topic: [PATCH] x86/i8259: Work around buggy legacy PIC Thread-Index: AQHXR3+B5Hf0DG1T80+Lb/Y+9zG7TarhDftggAATCoCAABWukIABrCMAgAATcQA= Date: Fri, 14 May 2021 13:13:19 +0000 Message-ID: References: <20210512210459.1983026-1-luzmaximilian@gmail.com> <9b70d8113c084848b8d9293c4428d71b@AcuMS.aculab.com> <87tun54gg3.ffs@nanos.tec.linutronix.de> In-Reply-To: <87tun54gg3.ffs@nanos.tec.linutronix.de> 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-kernel@vger.kernel.org From: Thomas Gleixner > Sent: 14 May 2021 14:02 > > David, > > On Thu, May 13 2021 at 10:36, David Laight wrote: > > >> -----Original Message----- > >> From: Maximilian Luz > > can you please fix your mail client and spare us the useless header > duplication in the reply? I have to delete them by hand - must have forgotten, I can't fix outlook :-) > > It is also worth noting that the probe code is spectacularly crap. > > It writes 0xff and then checks that 0xff is read back. > > Almost anything (including a failed PCIe read to the ISA bridge) > > will return 0xff and make the test pass. > > unsigned char probe_val = ~(1 << PIC_CASCADE_IR); > > outb(probe_val, PIC_MASTER_IMR); > new_val = inb(PIC_MASTER_IMR); > > How is that writing 0xFF? Sorry I misread the code and diagnostic output. In any case writing a value and expecting the same value back isn't exactly a high-quality probe. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)