linux-kernel - Re: [PATCH 2/2] PCI: vmd: Let OS control ASPM for devices under VMD domain

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Message-ID: <CAAd53p4NHoqt1=LsSpKS8CMF_-BHg-N_nCF3F5qZpkWDNohU1w@mail.gmail.com>
Date: Fri, 16 Aug 2024 14:17:04 +0800
From: Kai-Heng Feng <kai.heng.feng@...onical.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: bhelgaas@...gle.com, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, nirmal.patel@...ux.intel.com, 
	jonathan.derrick@...ux.dev, ilpo.jarvinen@...ux.intel.com, 
	david.e.box@...ux.intel.com
Subject: Re: [PATCH 2/2] PCI: vmd: Let OS control ASPM for devices under VMD domain

Hi Bjorn,

On Fri, Aug 2, 2024 at 9:04 AM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> On Fri, Aug 2, 2024 at 8:04 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
> >
> > On Thu, May 30, 2024 at 04:52:27PM +0800, Kai-Heng Feng wrote:
> > > Intel SoC cannot reach lower power states when mapped VMD PCIe bridges
> > > and NVMe devices don't have ASPM configured.
> > >
> > > So set aspm_os_control attribute to let OS really enable ASPM for those
> > > devices.
> > >
> > > Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR")
> >
> > I assume f492edb40b54 was tested and worked at the time.  Is the
> > implication that newer Intel SoCs have added more requirements for
> > getting to low power states, since __pci_enable_link_state() would
> > have warned and done nothing even then?
> >
> > Or maybe this is a new system that sets ACPI_FADT_NO_ASPM, and
> > f492edb40b54 was tested on systems that did *not* set
> > ACPI_FADT_NO_ASPM?
>
> I believe it's the case here. Vendors may or may not set
> ACPI_FADT_NO_ASPM, so f492edb40b54 works on some systems but not
> others.

Do you think this is code is ready? Or is there any improvement should be made?

Kai-Heng

>
> Kai-Heng
>
> >
> > > Link: https://lore.kernel.org/linux-pm/218aa81f-9c6-5929-578d-8dc15f83dd48@panix.com/
> > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > > ---
> > >  drivers/pci/controller/vmd.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > > index 87b7856f375a..1dbc525c473f 100644
> > > --- a/drivers/pci/controller/vmd.c
> > > +++ b/drivers/pci/controller/vmd.c
> > > @@ -751,6 +751,8 @@ static int vmd_pm_enable_quirk(struct pci_dev *pdev, void *userdata)
> > >       if (!(features & VMD_FEAT_BIOS_PM_QUIRK))
> > >               return 0;
> > >
> > > +     pdev->aspm_os_control = 1;
> > > +
> > >       pci_enable_link_state_locked(pdev, PCIE_LINK_STATE_ALL);
> > >
> > >       pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_LTR);
> > > --
> > > 2.43.0
> > >