From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758223AbbCDULK (ORCPT ); Wed, 4 Mar 2015 15:11:10 -0500 Received: from mail-wi0-f180.google.com ([209.85.212.180]:32850 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753968AbbCDULI (ORCPT ); Wed, 4 Mar 2015 15:11:08 -0500 Date: Wed, 4 Mar 2015 21:11:03 +0100 From: Ingo Molnar To: Arjan van de Ven Cc: Borislav Petkov , "Li, Aubrey" , "alan@linux.intel.com" , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "Rafael J. Wysocki" , Len.Brown@intel.com, x86@kernel.org, LKML Subject: Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced platform Message-ID: <20150304201102.GA6530@gmail.com> References: <54F67ACC.3010500@linux.intel.com> <20150304050858.GB5158@gmail.com> <54F69774.2050400@linux.intel.com> <20150304053106.GA3701@gmail.com> <54F6A08B.2010105@linux.intel.com> <20150304073717.GA11736@gmail.com> <54F6C59C.706@linux.intel.com> <20150304095011.GH3233@pd.tnic> <54F71888.4040608@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54F71888.4040608@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arjan van de Ven wrote: > On 3/4/2015 1:50 AM, Borislav Petkov wrote: > >On Wed, Mar 04, 2015 at 12:43:08AM -0800, Arjan van de Ven wrote: > >>> > >>>Using 'acpi_gbl_reduced_hardware' flag outside the ACPI code > >>>is a mistake. > >> > >>ideally, the presence of that flag in the firmware table will clear/set more global settings, > >>for example, having that flag should cause the 8042 input code to not probe for the 8042. > >> > >>for interrupts, there really ought to be a "apic first/only" mode, which is then used on > >>all modern systems (not just hw reduced). > > > >Do we need some sort of platform-specific querying interfaces now too, > >similar to cpu_has()? I.e., platform_has()... > > > > if (platform_has(X86_PLATFORM_REDUCED_HW)) > > do stuff.. > > more like > > platform_has(X86_PLATFORM_PIT) > > etc, one for each legacy io item Precisely. The main problem is the generic, 'lumps everything together' nature of the acpi_gbl_reduced_hardware flag. (Like the big kernel lock lumped together all sorts of locking rules and semantics.) Properly split out, feature-ish or driver-ish interfaces for PIT and other legacy details are the proper approach to 'turn them off'. - x86_platform is a function pointer driven, driver-ish interface. - platform_has(X86_PLATFORM_IT) is a flag driven, feature-flag-ish interface. Both are fine - for something as separate as the PIT (or the PIC) it might make more sense to go towards a 'driver' interface though, as modern drivers are (and will be) much different from the legacy PIT. Whichever method is used, low level platforms can just switch them on/off in their enumeration/detection routines, while the generic code will have them enabled by default. > so we can clear it on hw reduced, but also in other cases. hw > reduced is one way, but I'd be surprised if there weren't other ways > (like quirks) where we'd want to do the same things Exactly. The key step is the proper, clean separation out of hardware interfaces. Thanks, Ingo