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SubjectRe: [PATCH v2] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for X86_64
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.

So can we do a small change like below, so that we are able to disable
the HPET_TIMER in our own x86_64 .config, while all exising distributions
are not affected as it is still default "y" .

---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f67e839..a1027a5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -711,7 +711,7 @@ source "arch/x86/Kconfig.cpu"

config HPET_TIMER
def_bool X86_64
- prompt "HPET Timer Support" if X86_32
+ prompt "HPET Timer Support"
---help---
Use the IA-PC HPET (High Precision Event Timer) to manage
time in preference to the PIT and RTC, if a HPET is

Thanks,
Feng



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