From: Thomas Gleixner <tglx@linutronix.de>
To: Daniel Drake <drake@endlessm.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Hans de Goede <hdegoede@redhat.com>,
david.e.box@linux.intel.com,
Endless Linux Upstreaming Team <linux@endlessm.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
x86@kernel.org
Subject: Re: No 8254 PIT & no HPET on new Intel N3350 platforms causes kernel panic during early boot
Date: Wed, 3 Apr 2019 14:01:26 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1904031359530.1967@nanos.tec.linutronix.de> (raw)
In-Reply-To: <alpine.DEB.2.21.1904031206440.1967@nanos.tec.linutronix.de>
On Wed, 3 Apr 2019, Thomas Gleixner wrote:
> For newer CPUs we might assume that:
>
> 1) The TSC and APIC timer are actually usable
>
> 2) The frequencies can be retrieved from CPUID or MSRs
>
> If #1 and #2 are reliable we can avoid the whole calibration and interrupt
> delivery mess.
>
> That means we need the following decision logic:
>
> 1) If HPET is available in ACPI, boot normal.
>
> 2) If HPET is not available, verify that the PIT actually counts. If it
> does, boot normal.
>
> If it does not either:
>
> 2A) Verify that this is a PCH 300/C240 and fiddle with that ISST bit.
>
> But that means that we need to chase PCH ids forever...
>
> 2B) Shrug and just avoid the whole PIT/HPET magic all over the place:
>
> - Avoid the interrupt delivery check in the IOAPIC code as it's
> uninteresting in that case. Trivial to do.
>
> - Prevent the TSC calibration code from touching PIT/HPET. It
> should do that already when the TSC frequency can be retrieved
> via CPUID or MSR. Should work, emphasis on should ...
>
> See the mess in: native_calibrate_tsc() and the magic tables in
> tsc_msr.c how well that stuff works.
>
> The cpu_khz_from_cpuid() case at seems to not have these
> issues. Knock on wood!
>
> - Prevent the APIC calibration code from touching PIT/HPET. That's
> only happening right now when the TSC frequency comes from
> the MSRs. No idea why the CPUID method does not provide that.
>
> CPUID leaf 0x16 provides the bus frequency, so we can deduce the
> APIC timer frequency from there and spare the whole APIC timer
> calibration mess:
>
> ECX Bits 15 - 00: Bus (Reference) Frequency (in MHz).
>
> It's usually not required on these newer CPUs because they
> support TSC deadline timer, but you can disable that on the
> kernel command line and some implementations of that were
> broken. With that we are back to square one.
>
> So we need to make sure that these things work under all
> circumstances.
>
> Rafael?
And we have to think hard about how we are going to provide that for
backporting in a digestable form. People are supposed to run recent stable
kernels (I'm not talking about dead kernels ...).
Thanks,
tglx
next prev parent reply other threads:[~2019-04-03 12:01 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 7:49 No 8254 PIT & no HPET on new Intel N3350 platforms causes kernel panic during early boot Daniel Drake
2019-04-03 11:21 ` Thomas Gleixner
2019-04-03 12:01 ` Thomas Gleixner [this message]
2019-04-09 5:43 ` Daniel Drake
2019-04-10 12:54 ` Thomas Gleixner
2019-04-16 5:21 ` Daniel Drake
2019-05-09 10:35 ` [tip:x86/apic] x86/tsc: Set LAPIC timer period to crystal clock frequency tip-bot for Daniel Drake
2019-06-27 8:54 ` No 8254 PIT & no HPET on new Intel N3350 platforms causes kernel panic during early boot Daniel Drake
2019-06-27 14:06 ` Thomas Gleixner
2019-06-28 3:33 ` Daniel Drake
2019-06-28 5:07 ` Thomas Gleixner
2019-04-17 5:28 Detecting x86 LAPIC timer frequency from CPUID data Daniel Drake
2019-04-18 13:12 ` Thomas Gleixner
2019-04-18 22:30 ` Thomas Gleixner
2019-04-19 8:35 ` Daniel Drake
2019-04-19 8:57 ` Thomas Gleixner
2019-04-19 20:50 ` Jacob Pan
2019-04-19 20:52 ` Thomas Gleixner
2019-04-19 23:09 ` Jacob Pan
2019-05-09 10:34 ` [tip:x86/apic] x86/tsc: Use CPUID.0x16 to calculate missing crystal frequency tip-bot for Daniel Drake
2019-05-09 5:54 [PATCH v2 1/3] x86/tsc: use " Daniel Drake
2019-05-09 5:54 ` [PATCH v2 2/3] x86/apic: rename lapic_timer_frequency to lapic_timer_period Daniel Drake
2019-05-09 10:34 ` [tip:x86/apic] x86/apic: Rename 'lapic_timer_frequency' to 'lapic_timer_period' tip-bot for Daniel Drake
2019-05-09 5:54 ` [PATCH v2 3/3] x86/tsc: set LAPIC timer period to crystal clock frequency Daniel Drake
2019-05-09 7:25 ` [PATCH v2 1/3] x86/tsc: use CPUID.0x16 to calculate missing crystal frequency Thomas Gleixner
2019-05-09 9:07 ` Ingo Molnar
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