* Arjan van de Ven <ar...@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.
> 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
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