From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752278AbbCEMmo (ORCPT ); Thu, 5 Mar 2015 07:42:44 -0500 Received: from mga01.intel.com ([192.55.52.88]:48655 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751105AbbCEMmn (ORCPT ); Thu, 5 Mar 2015 07:42:43 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,346,1422950400"; d="scan'208";a="536494170" Message-ID: <54F84F3A.8080902@linux.intel.com> Date: Thu, 05 Mar 2015 20:42:34 +0800 From: "Li, Aubrey" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Ingo Molnar 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 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> <20150305113641.GB23046@gmail.com> In-Reply-To: <20150305113641.GB23046@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/3/5 19:36, Ingo Molnar wrote: > > * 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(). > I'll do more investigation above items but I want to leave at least these two as the quirk today unless I am convinced I can do that because from my understanding, UEFI runtime services should not be supported in reduced hw mode. > etc. > > Just keep the generic init codepaths free of those random selections > based on global flags, okay? > Agree. Thanks, -Aubrey > Thanks, > > Ingo > >