Messages in this thread Patch in this message | | | Date | Tue, 10 Mar 2015 07:26:03 +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 20:42, Li, Aubrey wrote: > 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. >>
how about this one?
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index b9e30da..70955d6 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -1541,6 +1541,16 @@ int __init early_acpi_boot_init(void) */ early_acpi_process_madt();
+ /* + * Override x86_init functions and bypass legacy pic + * in hardware-reduced ACPI mode + */ + if (acpi_gbl_reduced_hardware) { + x86_init.timers.timer_init = x86_init_noop; + x86_init.irqs.pre_vector_init = x86_init_noop; + legacy_pic = &null_legacy_pic; + } + return 0; }
>> - 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. >
If the above makes sense, I'll send poweroff and reboot change together in a seperate patch.
Thanks, -Aubrey
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