[PATCH 3/4] PCI/PM: Always disable PTM for all devices during suspend

Bjorn Helgaas
2022-09-02T15:26:18Z

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.

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 | 8 ++++++++
drivers/pci/pci.c | 20 --------------------
2 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 2815922ac525..f07399a94807 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);
+
pci_dev->skip_bus_pm = false;

if (pci_has_legacy_pm_support(pci_dev))
@@ -1269,6 +1275,8 @@ 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.
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);
--
2.25.1