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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Sat, 3 Sep 2022 19:13:49 +0200
Message-ID: <CAJZ5v0iScCTtWMv2j=AuK4od0G-4aCJuYY=oWnfVVnAhe32QVg@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] PCI/PM: Always disable PTM for all devices during suspend
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>
Cc:     Kai-Heng Feng <kai.heng.feng@canonical.com>,
        Rajvi Jingar <rajvi.jingar@linux.intel.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Koba Ko <koba.ko@canonical.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        "David E . Box" <david.e.box@linux.intel.com>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>
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On Sat, Sep 3, 2022 at 1:59 AM Sathyanarayanan Kuppuswamy
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
>
>
> On 9/2/22 4:35 PM, Bjorn Helgaas wrote:
> > From: Bjorn Helgaas <bhelgaas@google.com>
> >
> > 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.
> >
> > That means we also have to disable PTM on downstream devices.  PCIe r6.0,
> > sec 2.2.8, recommends that functions support generation of messages in
> > non-D0 states, so we have to 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).
> >
> > PTM was previously disabled only for Root Ports, and it was disabled in
> > pci_prepare_to_sleep(), which is not called at all if a driver supports
> > legacy PM or does its own state saving.
> >
> > Instead, disable PTM early in pci_pm_suspend() and pci_pm_runtime_suspend()
> > so we do it in all cases.
> >
> > Previously PTM was disabled *after* saving device state, so the state
> > restore on resume automatically re-enabled it.  Since we now disable PTM
> > *before* saving state, we must explicitly re-enable it.
> >
> > Here's a sample of errors that occur when PTM is disabled only on the Root
> > Port.  With this topology:
> >
> >   0000:00:1d.0 Root Port            to [bus 08-71]
> >   0000:08:00.0 Switch Upstream Port to [bus 09-71]
> >
> > Kai-Heng reported errors like this:
> >
> >   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
> >
> > Decoding TLP header 0x34...... (0011 0100b) and 0x08000052:
> >
> >   Fmt                         001b  4 DW header, no data
> >   Type                     1 0100b  Msg (Local - Terminate at Receiver)
> >   Requester ID  0x0800              Bus 08 Devfn 00.0
> >   Message Code    0x52  0101 0010b  PTM Request
> >
> > The 00:1d.0 Root Port logged an Unsupported Request error when it received
> > a PTM Request with Requester ID 08:00.0.
> >
> > Fixes: a697f072f5da ("PCI: Disable PTM during suspend to save power")
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215453
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216210
> > Based-on: https://lore.kernel.org/r/20220706123244.18056-1-kai.heng.feng@canonical.com
> > Based-on-patch-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> > Reported-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > ---
> >  drivers/pci/pci-driver.c | 14 ++++++++++++++
> >  drivers/pci/pci.c        | 20 --------------------
> >  2 files changed, 14 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > index 2815922ac525..115febaa7e0b 100644
> > --- a/drivers/pci/pci-driver.c
> > +++ b/drivers/pci/pci-driver.c
> > @@ -772,6 +772,12 @@ static int pci_pm_suspend(struct device *dev)
> >       struct pci_dev *pci_dev = to_pci_dev(dev);
> >       const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> >
> > +     /*
> > +      * Disabling PTM allows some systems, e.g., Intel mobile chips
> > +      * since Coffee Lake, to enter a lower-power PM state.
> > +      */
> > +     pci_disable_ptm(pci_dev);
>
> I think you can use "if (pci_dev->ptm_enabled)" check for pci_disable_ptm()
> as well. This will avoid unnecessary checks in pci_disable_ptm().

Or use that check in pci_disable_ptm() instead of the pci_is_pcie() one.

Also, I would remae pci_disable_ptm() to pci_suspend_ptm() (because
its role is to temporarily disable PTM for system-wide suspend) and
introduc pci_resume_ptm() that will do

if (pci_dev->ptm_enabled)
        pci_enable_ptm(pci_dev, NULL);

> > +
> >       pci_dev->skip_bus_pm = false;
> >
> >       if (pci_has_legacy_pm_support(pci_dev))
> > @@ -982,6 +988,9 @@ static int pci_pm_resume(struct device *dev)
> >       if (pci_dev->state_saved)
> >               pci_restore_standard_config(pci_dev);
> >
> > +     if (pci_dev->ptm_enabled)
> > +             pci_enable_ptm(pci_dev, NULL);
> > +
> >       if (pci_has_legacy_pm_support(pci_dev))
> >               return pci_legacy_resume(dev);
> >
> > @@ -1269,6 +1278,8 @@ static int pci_pm_runtime_suspend(struct device *dev)
> >       pci_power_t prev = pci_dev->current_state;
> >       int error;
> >
> > +     pci_disable_ptm(pci_dev);
> > +
> >       /*
> >        * If pci_dev->driver is not set (unbound), we leave the device in D0,
> >        * but it may go to D3cold when the bridge above it runtime suspends.
> > @@ -1331,6 +1342,9 @@ static int pci_pm_runtime_resume(struct device *dev)
> >        */
> >       pci_pm_default_resume_early(pci_dev);
> >
> > +     if (pci_dev->ptm_enabled)
> > +             pci_enable_ptm(pci_dev, NULL);
> > +
> >       if (!pci_dev->driver)
> >               return 0;
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 95bc329e74c0..b0e2968c8cca 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -2706,16 +2706,6 @@ int pci_prepare_to_sleep(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);
> > -
> >       pci_enable_wake(dev, target_state, wakeup);
> >
> >       error = pci_set_power_state(dev, target_state);
> > @@ -2764,16 +2754,6 @@ 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);
> > -
> >       __pci_enable_wake(dev, target_state, pci_dev_run_wake(dev));
> >
> >       error = pci_set_power_state(dev, target_state);
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer