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Date:   Mon, 11 Oct 2021 06:59:31 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH 5.4 51/52] x86/hpet: Use another crystalball to evaluate
 HPET usability
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References: <20211011134503.715740503@linuxfoundation.org>
        <20211011134505.483011431@linuxfoundation.org>
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On Mon, 11 Oct 2021 15:46:20 +0200 Greg Kroah-Hartman wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> commit 6e3cd95234dc1eda488f4f487c281bac8fef4d9b upstream.
> 
> On recent Intel systems the HPET stops working when the system reaches PC10
> idle state.
> 
> The approach of adding PCI ids to the early quirks to disable HPET on
> these systems is a whack a mole game which makes no sense.
> 
> Check for PC10 instead and force disable HPET if supported. The check is
> overbroad as it does not take ACPI, intel_idle enablement and command
> line parameters into account. That's fine as long as there is at least
> PMTIMER available to calibrate the TSC frequency. The decision can be
> overruled by adding "hpet=force" on the kernel command line.
> 
> Remove the related early PCI quirks for affected Ice Cake and Coffin Lake
> systems as they are not longer required. That should also cover all
> other systems, i.e. Tiger Rag and newer generations, which are most
> likely affected by this as well.
> 
> Fixes: Yet another hardware trainwreck
> Reported-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: Jakub Kicinski <kuba@kernel.org>
> Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>
> Cc: stable@vger.kernel.org
> Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

FWIW I've never seen any problems prior to Paul's rework of bad clock
detection in 5.13. Backports to 5.4 and 5.10 are not necessary.