Date:   Wed, 24 Aug 2022 15:26:00 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     bhelgaas@...gle.com, mika.westerberg@...ux.intel.com,
        koba.ko@...onical.com,
        "David E . Box" <david.e.box@...ux.intel.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: Disable upstream port PTM during suspend

On Sat, Aug 20, 2022 at 7:49 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Wed, Jul 06, 2022 at 08:32:44PM +0800, Kai-Heng Feng wrote:
> > On Intel Alder Lake platforms, Thunderbolt entering D3cold can cause
> > some errors reported by AER:
>
> What's the connection with Thunderbolt?  I see "thunderbolt
> 0000:0a:00.0" in dmesg, but I think we see that message only because
> 0a:00.0 happens to be in the hierarchy below the 00:1d.0 Root Port,
> not specifically because it's a Thunderbolt device.

I mentioned "Thunderbolt" because those bridge devices are part of
Thunderbolt chip. Sorry for the confusing.

>
> Here's the hierarchy:
>
>   0000:00:1d.0 Root Port              to [bus 08-71]
>   0000:08:00.0 Switch Upstream Port   to [bus 09-71]
>   0000:09:00.0 Switch Downstream Port to [bus 0a]
>   0000:0a:00.0 Endpoint (USB controller)
>   0000:09:01.0 Switch Downstream Port to [bus 0b-3d]
>   0000:09:02.0 Switch Downstream Port to [bus 3e]
>   0000:3e:00.0 Endpoint (USB controller)
>   0000:09:03.0 Switch Downstream Port to [bus 3f-71]
>
> The error logged by 00:1d.0 is an Unsupported Request with Requester
> ID 08:00.0.
>
> I think the only relevant thing is that 08:00.0 has PTM enabled and
> 00:1d.0 has PTM disabled because pci_prepare_to_sleep() only disables
> PTM for Root Ports.  The same thing could happen if 08:00.0 were an
> Endpoint or a non-Thunderbolt Switch Upstream Port.
>
> Is entering D3cold relevant here?  I don't know how to tell from dmesg
> that we're entering D3cold.  If we actually put 08:00.0 in D3cold, I
> don't think we would see the Unsupported Request because 08:00.0 can't
> send PTM requests from D3cold.

Right, the D3cold is achieved when power resources of 00:1d.0 is off.
So when the PTM request is logged, 08:00.0 is still at D3hot.

>
> > pcieport 0000:00:1d.0: AER: Uncorrected (Non-Fatal) error received: 0000:00:1d.0
> > pcieport 0000:00:1d.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Requester ID)
> > pcieport 0000:00:1d.0:   device [8086:7ab0] error status/mask=00100000/00004000
> > pcieport 0000:00:1d.0:    [20] UnsupReq               (First)
> > pcieport 0000:00:1d.0: AER:   TLP Header: 34000000 08000052 00000000 00000000
> > thunderbolt 0000:0a:00.0: AER: can't recover (no error_detected callback)
> > xhci_hcd 0000:3e:00.0: AER: can't recover (no error_detected callback)
> > pcieport 0000:00:1d.0: AER: device recovery failed
> >
> > In addition to that, it can also block system from suspending when
> > a Thunderbolt dock is attached to the same system.
>
>
> > The original approach [1] is to disable AER and DPC when link is in
> > L2/L3 Ready, L2 and L3, but Bjorn identified the root cause is the Unsupported
> > Request:
> >   - 08:00.0 sent a PTM Request Message (a Posted Request)
> >   - 00:1d.0 received the PTM Request Message
> >   - The link transitioned to DL_Down
> >   - Per sec 2.9.1, 00:1d.0 discarded the Request and reported an
> >     Unsupported Request
> >   - Or, per sec 6.21.3, if 00:1d.0 received a PTM Request when its
> >     own PTM Enable was clear, it would also be treated as an
> >     Unsupported Request
> >
> > And further: 'David did something like this [1], but just for Root Ports. That
> > looks wrong to me because sec 6.21.3 says we should not have PTM enabled in an
> > Upstream Port (i.e., in a downstream device like 08:00.0) unless it is already
> > enabled in the Downstream Port (i.e., in the Root Port 00:1d.0).'
> >
> > So also disable upstream port PTM to make the PCI driver conform to the spec
> > and solve the issue.
> >
> > [1] https://lore.kernel.org/all/20220408153159.106741-1-kai.heng.feng@canonical.com/
> > [2] https://lore.kernel.org/all/20220422222433.GA1464120@bhelgaas/
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215453
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216210
> > Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > Cc: David E. Box <david.e.box@...ux.intel.com>
> > Cc: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>
> >
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> > ---
> >  drivers/pci/pci.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index cfaf40a540a82..8ba8a0e12946e 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -2717,7 +2717,8 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
> >        * port to enter a lower-power PM state and the SoC to reach a
> >        * lower-power idle state as a whole.
> >        */
> > -     if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> > +     if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> > +         pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM)
> >               pci_disable_ptm(dev);
> >
> >       pci_enable_wake(dev, target_state, wakeup);
> > @@ -2775,7 +2776,8 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
> >        * port to enter a lower-power PM state and the SoC to reach a
> >        * lower-power idle state as a whole.
> >        */
> > -     if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> > +     if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> > +         pci_pcie_type(dev) == PCI_EXP_TYPE_UPSTREAM)
> >               pci_disable_ptm(dev);
> >
> >       __pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
>
> What do you think of the following possible rework?  I think it's
> functionally the same except that it disables PTM on Endpoints as well
> as Switch Upstream Ports.

Your rework works for me, with much better comment :)

Tested-by: Kai-Heng Feng <kai.heng.feng@...onical.com>

>
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95bc329e74c0..96487a9ce5bf 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2707,14 +2707,19 @@ int pci_prepare_to_sleep(struct pci_dev *dev)
>                 return -EIO;
>
>         /*
> -        * There are systems (for example, Intel mobile chips since Coffee
> -        * Lake) where the power drawn while suspended can be significantly
> -        * reduced by disabling PTM on PCIe root ports as this allows the
> -        * port to enter a lower-power PM state and the SoC to reach a
> -        * lower-power idle state as a whole.
> +        * We want to disable PTM on Root Ports because that allows some
> +        * chips, e.g., Intel mobile chips since Coffee Lake, to enter a
> +        * lower-power PM state.
> +        *
> +        * PCIe r6.0, sec 2.2.8, strongly recommends that functions support
> +        * generation of messages in non-D0 states, so we assume Switch
> +        * Upstream Ports or Endpoints may send PTM Requests while in D1,
> +        * D2, and D3hot.  A PTM message received by a Downstream Port
> +        * (including a Root Port) with PTM disabled must be treated as an
> +        * Unsupported Request (sec 6.21.3).  To prevent this error,
> +        * disable PTM in *all* devices, not just Root Ports.
>          */
> -       if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> -               pci_disable_ptm(dev);
> +       pci_disable_ptm(dev);
>
>         pci_enable_wake(dev, target_state, wakeup);
>
> @@ -2764,15 +2769,8 @@ int pci_finish_runtime_suspend(struct pci_dev *dev)
>         if (target_state == PCI_POWER_ERROR)
>                 return -EIO;
>
> -       /*
> -        * There are systems (for example, Intel mobile chips since Coffee
> -        * Lake) where the power drawn while suspended can be significantly
> -        * reduced by disabling PTM on PCIe root ports as this allows the
> -        * port to enter a lower-power PM state and the SoC to reach a
> -        * lower-power idle state as a whole.
> -        */
> -       if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> -               pci_disable_ptm(dev);
> +       /* See rationale above for disabling PTM */
> +       pci_disable_ptm(dev);
>
>         __pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
>
> diff --git a/drivers/pci/pcie/ptm.c b/drivers/pci/pcie/ptm.c
> index 368a254e3124..ec338470d13f 100644
> --- a/drivers/pci/pcie/ptm.c
> +++ b/drivers/pci/pcie/ptm.c
> @@ -31,12 +31,18 @@ static void pci_ptm_info(struct pci_dev *dev)
>
>  void pci_disable_ptm(struct pci_dev *dev)
>  {
> -       int ptm;
> +       int type, ptm;
>         u16 ctrl;
>
>         if (!pci_is_pcie(dev))
>                 return;
>
> +       type = pci_pcie_type(dev);
> +       if (!(type == PCI_EXP_TYPE_ROOT_PORT ||
> +             type == PCI_EXP_TYPE_UPSTREAM ||
> +             type == PCI_EXP_TYPE_ENDPOINT))
> +               return;
> +
>         ptm = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_PTM);
>         if (!ptm)
>                 return;

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