From: Bjorn Helgaas <helgaas@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
Feng Tang <feng.tang@intel.com>,
Kai-Heng Feng <kai.heng.feng@canonical.com>
Subject: Re: [PATCH] x86/PCI: Convert force_disable_hpet() to standard quirk
Date: Wed, 25 Nov 2020 13:13:27 -0600 [thread overview]
Message-ID: <20201125191327.GA653914@bjorn-Precision-5520> (raw)
In-Reply-To: <87v9dtk3j4.fsf@nanos.tec.linutronix.de>
On Wed, Nov 25, 2020 at 01:46:23PM +0100, Thomas Gleixner wrote:
> On Thu, Nov 19 2020 at 12:19, Bjorn Helgaas wrote:
> > 62187910b0fc ("x86/intel: Add quirk to disable HPET for the Baytrail
> > platform") implemented force_disable_hpet() as a special early quirk.
> > These run before the PCI core is initialized and depend on the
> > x86/pci/early.c accessors that use I/O ports 0xcf8 and 0xcfc.
> >
> > But force_disable_hpet() doesn't need to be one of these special early
> > quirks. It merely sets "boot_hpet_disable", which is tested by
> > is_hpet_capable(), which is only used by hpet_enable() and hpet_disable().
> > hpet_enable() is an fs_initcall(), so it runs after the PCI core is
> > initialized.
>
> hpet_enable() is not an fs_initcall(). hpet_late_init() is and that
> invokes hpet_enable() only for the case that ACPI did not advertise it
> and the force_hpet quirk provided a base address.
>
> But hpet_enable() is also invoked via:
>
> start_kernel()
> late_time_init()
> x86_late_time_init()
> hpet_time_init()
>
> which is way before the PCI core is available and we really don't want
> to set it up there if it's known to be broken :)
Wow, I really blew that, don't know how I missed that path. Thanks
for catching this! I'll drop this patch.
> Now the more interesting question is why this needs to be a PCI quirk in
> the first place. Can't we just disable the HPET based on family/model
> quirks?
You mean like a CPUID check or something? I'm all in favor of doing
something that doesn't depend on PCI.
> e0748539e3d5 ("x86/intel: Disable HPET on Intel Ice Lake platforms")
> f8edbde885bb ("x86/intel: Disable HPET on Intel Coffee Lake H platforms")
> fc5db58539b4 ("x86/quirks: Disable HPET on Intel Coffe Lake platforms")
> 62187910b0fc ("x86/intel: Add quirk to disable HPET for the Baytrail platform")
>
> I might be missing something here, but in general on anything modern
> HPET is mostly useless.
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2020-11-25 19:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 18:19 [PATCH] x86/PCI: Convert force_disable_hpet() to standard quirk Bjorn Helgaas
2020-11-24 23:27 ` Bjorn Helgaas
2020-11-25 12:46 ` Thomas Gleixner
2020-11-25 19:13 ` Bjorn Helgaas [this message]
2020-11-26 0:50 ` Thomas Gleixner
2020-11-26 1:24 ` Feng Tang
2020-11-26 23:27 ` Thomas Gleixner
2020-11-27 6:11 ` Feng Tang
2020-11-30 19:21 ` Thomas Gleixner
2020-12-01 8:34 ` Feng Tang
2020-12-02 7:28 ` Zhang Rui
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