Messages in this thread | | | Date | Thu, 05 Mar 2015 20:42:34 +0800 | From | "Li, Aubrey" <> | Subject | Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced platform |
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On 2015/3/5 19:36, Ingo Molnar wrote: > > * Li, Aubrey <aubrey.li@linux.intel.com> wrote: > >> On 2015/3/5 4:11, Ingo Molnar wrote: >>> >>> * Arjan van de Ven <arjan@linux.intel.com> 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 > >
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