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SubjectRe: [PATCH v2] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for X86_64
On Tue, Apr 15, 2014 at 12:42:06PM +0200, Ingo Molnar wrote:
>
> * Feng Tang <feng.tang@intel.com> wrote:
>
> > On Tue, Apr 15, 2014 at 11:00:25AM +0200, Ingo Molnar wrote:
> > >
> > > * Feng Tang <feng.tang@intel.com> wrote:
> > >
> > > > Hi Ingo,
> > > >
> > > > On Fri, Mar 28, 2014 at 09:11:17AM +0100, Ingo Molnar wrote:
> > > > >
> > > > > * Clemens Ladisch <clemens@ladisch.de> wrote:
> > > > >
> > > > > > Feng Tang wrote:
> > > > > > > On Fri, Mar 28, 2014 at 08:17:16AM +0100, Ingo Molnar wrote:
> > > > > > >> * Feng Tang <feng.tang@intel.com> wrote:
> > > > > > >> - or the kernel should have a quirk to reliably disable it. Why
> > > > > > >> should we crash or misbehave if a driver is built into the
> > > > > > >> kernel?
> > > > > > >
> > > > > > > I thought about this before, HPET doesn't have PCI ID like stuff,
> > > > > >
> > > > > > HPET does have the PCI vendor ID in the first register.
> > > > > >
> > > > > > > only thing I can think of to identify them may be the CPU family/ID.
> > > > > >
> > > > > > The HPET is implemented by some actual chip, and that chip also has lots
> > > > > > of PCI devices. (In the case of a SoC, the CPU ID would work, too).
> > > > >
> > > > > Correct. See arch/x86/kernel/hpet.c, which has a large number of HPET
> > > > > quirks keyed off chipset PCI IDs:
> > > > >
> > > > > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_ESB2_0,
> > > > > ich_force_enable_hpet);
> > > > > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_ICH6_0,
> > > > > ich_force_enable_hpet);
> > > > > DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_ICH6_1,
> > > > > ich_force_enable_hpet);
> > > > > [...]
> > > >
> > > > I just gave it another thought, that the HPET on our platform
> > > > currently do have some problem to be used as clocksource/clockevent,
> > > > but it may get fixed in future version (by Silicon or BIOS).
> > > >
> > > > If I add quirk to block it now, I may revert this code in future
> > > > when it get fixed, same problem applis for the future generation of
> > > > platform.
> > >
> > > If the hardware or BIOS gets fixed then that will be visible in the
> > > revision level of the hardware, right?
> >
> > AFAIK, if it is fixed in a new silicon version, we should be able to
> > detect it by the "stepping", but the PCI DEV ID is not likely to
> > change.
> >
> > If it is fixed by BIOS or PUNIT FW, then we may go through the DMI
> > info to check the BIOS version, One problem is there is some
> > Baytrail tablet platforms that doesn't provide DMI info as its FW is
> > not UEFI/Legacy BIOS compatible version.
>
> So just turn it off for the current hardware, via PCI ID. When you get
> a fix, you can turn it back on again by refining the quirk check, for
> that specific hardware.

got it, thanks!

- Feng



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