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Date: Fri, 2 Sep 2022 16:59:20 -0700
From: Sathyanarayanan Kuppuswamy
<sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Bjorn Helgaas <helgaas@...nel.org>,
Kai-Heng Feng <kai.heng.feng@...onical.com>,
Rajvi Jingar <rajvi.jingar@...ux.intel.com>,
"Rafael J . Wysocki" <rafael@...nel.org>
Cc: Koba Ko <koba.ko@...onical.com>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
"David E . Box" <david.e.box@...ux.intel.com>,
linux-pci@...r.kernel.org, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2 3/3] PCI/PM: Always disable PTM for all devices during
suspend
On 9/2/22 4:35 PM, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.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@...onical.com>
> Reported-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.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().
> +
> 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
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