linux-kernel - Re: [PATCH 5.4 51/52] x86/hpet: Use another crystalball to evaluate HPET usability

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Date:   Mon, 11 Oct 2021 16:05:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 5.4 51/52] x86/hpet: Use another crystalball to evaluate
 HPET usability

On Mon, Oct 11, 2021 at 06:59:31AM -0700, Jakub Kicinski wrote:
> On Mon, 11 Oct 2021 15:46:20 +0200 Greg Kroah-Hartman wrote:
> > From: Thomas Gleixner <tglx@...utronix.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@...nel.org>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Tested-by: Jakub Kicinski <kuba@...nel.org>
> > Reviewed-by: Rafael J. Wysocki <rafael@...nel.org>
> > Cc: stable@...r.kernel.org
> > Cc: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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.

Given that the hardware is still just as broken in those older kernels,
why not?

thanks,

greg k-h