From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755235AbbCELgs (ORCPT ); Thu, 5 Mar 2015 06:36:48 -0500 Received: from mail-we0-f169.google.com ([74.125.82.169]:45327 "EHLO mail-we0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbbCELgr (ORCPT ); Thu, 5 Mar 2015 06:36:47 -0500 Date: Thu, 5 Mar 2015 12:36:41 +0100 From: Ingo Molnar To: "Li, Aubrey" Cc: Arjan van de Ven , Borislav Petkov , "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: <20150305113641.GB23046@gmail.com> References: <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> <20150304201102.GA6530@gmail.com> <54F83A61.3090906@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54F83A61.3090906@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 * Li, Aubrey wrote: > On 2015/3/5 4:11, Ingo Molnar wrote: > > > > * 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. > > Whichever method is used, we will face a problem how to determine > PIT exists or not. > > When we enabled Bay Trail-T platform at the beginning, we were > trying to make the code as generic as possible, and it works > properly up to now. So we don't have a SUBARCH like > X86_SUBARCH_INTEL_MID to use the platform specific functions. And > for now I'm not quite sure it's a good idea to create one. > > If we make it as a flag driven, I don't know there is a flag in > firmware better than ACPI HW reduced flag(Of course it's not good > enough to cover all the cases). Or if we want to use platform info > to turn on/off this flag, we'll have to maintain a platform list, > which may be longer and more complicated than worth doing that. Well, it's not nearly so difficult, because you already have a platform flag: acpi_gbl_reduced_hardware. What I object against is to infest generic codepaths with unreadable, unrobust crap like: + if (acpi_gbl_reduced_hardware) { + pr_info("Using NULL legacy PIC\n"); + legacy_pic = &null_legacy_pic; + } else + legacy_pic->init(0); To solve that, add a small (early) init function (say 'x86_reduced_hw_init()') that sets up the right driver selections if acpi_gbl_reduced_hardware is set: - in x86_reduced_hw_init() set 'legacy_pic' to 'null_legacy_pic' - clean up 'global_clock_event' handling: instead of a global variable, move its management into x86_platform_ops::get_clockevent() and set the method to hpet/pit/abp/etc. specific handlers that return the right clockevent device. - in your x86_reduced_hw_init() function add the hpet clockevent device to x86_platform_ops::get_clockevent, overriding the default PIT. - in x86_reduced_hw_init() set pm_power_off. - set 'reboot_type' and remove the acpi_gbl_reduced_hardware hack from efi_reboot_required(). etc. Just keep the generic init codepaths free of those random selections based on global flags, okay? Thanks, Ingo