Re: [PATCH] x86/intel: Disable HPET on another Intel Coffee Lake platform

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Sep 16, 2021 at 06:17:39AM -0700, Jakub Kicinski wrote:
> My Lenovo T490s with i7-8665U had been marking TSC as unstable
> since v5.13, resulting in very sluggish desktop experience...

Including the actual dmesg log line here might help others locate this
fix.

> I have a 8086:3e34 bridge, also known as "Host bridge: Intel
> Corporation Coffee Lake HOST and DRAM Controller (rev 0c)".
> Add it to the list.
> 
> We should perhaps consider applying this quirk more widely.
> The Intel documentation does not list my device [1], but
> linuxhw [2] does, and it seems to list a few more bridges
> we do not currently cover (3e31, 3ecc, 3e35, 3e0f).

In the fine tradition of:

  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 plat
form")

This seems to be an ongoing issue, not just a point defect in a single
product, and I really hate the onesy-twosy nature of this.  Is there
really no way to detect this issue automatically or fix whatever Linux
bug makes us trip over this?  I am no clock expert, so I have
absolutely no idea whether this is possible.

> [1] https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/8th-gen-core-family-datasheet-vol-2.pdf
> [2] https://github.com/linuxhw/DevicePopulation/blob/master/README.md
> 
> Cc: stable@vger.kernel.org # v5.13+

How did you pick v5.13?  force_disable_hpet() was added by
62187910b0fc ("x86/intel: Add quirk to disable HPET for the Baytrail
platform"), which appeared in v3.15.

> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> ---
>  arch/x86/kernel/early-quirks.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 38837dad46e6..7d2de04f8750 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -716,6 +716,8 @@ static struct chipset early_qrk[] __initdata = {
>  		PCI_CLASS_BRIDGE_HOST, PCI_ANY_ID, 0, force_disable_hpet},
>  	{ PCI_VENDOR_ID_INTEL, 0x3e20,
>  		PCI_CLASS_BRIDGE_HOST, PCI_ANY_ID, 0, force_disable_hpet},
> +	{ PCI_VENDOR_ID_INTEL, 0x3e34,
> +		PCI_CLASS_BRIDGE_HOST, PCI_ANY_ID, 0, force_disable_hpet},
>  	{ PCI_VENDOR_ID_INTEL, 0x3ec4,
>  		PCI_CLASS_BRIDGE_HOST, PCI_ANY_ID, 0, force_disable_hpet},
>  	{ PCI_VENDOR_ID_INTEL, 0x8a12,
> -- 
> 2.31.1
>