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Subject[RFC][PATCH v3 1/3]: PCI: PCIe links may not get configured for ASPM under POWERSAVE mode
Date

v3 -> v2: Moved ASPM enabling logic to pci_set_power_state()
v2 -> v1: Preserved the logic in pci_raw_set_power_state()
: Added ASPM enabling logic after scanning Root Bridge
: http://marc.info/?l=linux-pci&m=130046996216391&w=2
v1 : http://marc.info/?l=linux-pci&m=130013164703283&w=2

The assumption made in commit 41cd766b065970ff6f6c89dd1cf55fa706c84a3d
(PCI: Don't enable aspm before drivers have had a chance to veto it) that
pci_enable_device() will result in re-configuring ASPM when aspm_policy is
POWERSAVE is no longer valid. This is due to commit
97c145f7c87453cec90e91238fba5fe2c1561b32 (PCI: read current power state
at enable time) which resets dev->current_state to D0. Due to this the
call to pcie_aspm_pm_state_change() is never made. Note the equality check
(below) that returns early:
./drivers/pci/pci.c: pci_raw_set_pci_power_state()
546 /* Check if we're already there */
547 if (dev->current_state == state)
548 return 0;
Therefore OSPM never configures the PCIe links for ASPM to turn them "on".

Fix it by configuring ASPM from the pci_enable_device() code path. This
also allows a driver such as the e1000e networking driver a chance to
disable ASPM (L0s, L1), if need be, prior to enabling the device. A
driver may perform this action if the device is known to mis-behave
wrt ASPM.

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>

---
drivers/pci/pci.c | 6 ++++++
drivers/pci/pcie/aspm.c | 22 ++++++++++++++++++++++
include/linux/pci-aspm.h | 4 ++++
3 files changed, 32 insertions(+), 0 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b714d78..2472e71 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -740,6 +740,12 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state)

if (!__pci_complete_power_transition(dev, state))
error = 0;
+ /*
+ * When aspm_policy is "powersave" this call ensures
+ * that ASPM is configured.
+ */
+ if (!error && dev->bus->self)
+ pcie_aspm_powersave_config_link(dev->bus->self);

return error;
}
diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 3188cd9..e768620 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -707,6 +707,28 @@ void pcie_aspm_pm_state_change(struct pci_dev *pdev)
up_read(&pci_bus_sem);
}

+void pcie_aspm_powersave_config_link(struct pci_dev *pdev)
+{
+ struct pcie_link_state *link = pdev->link_state;
+
+ if (aspm_disabled || !pci_is_pcie(pdev) || !link)
+ return;
+
+ if (aspm_policy != POLICY_POWERSAVE)
+ return;
+
+ if ((pdev->pcie_type != PCI_EXP_TYPE_ROOT_PORT) &&
+ (pdev->pcie_type != PCI_EXP_TYPE_DOWNSTREAM))
+ return;
+
+ down_read(&pci_bus_sem);
+ mutex_lock(&aspm_lock);
+ pcie_config_aspm_path(link);
+ pcie_set_clkpm(link, policy_to_clkpm_state(link));
+ mutex_unlock(&aspm_lock);
+ up_read(&pci_bus_sem);
+}
+
/*
* pci_disable_link_state - disable pci device's link state, so the link will
* never enter specific states
diff --git a/include/linux/pci-aspm.h b/include/linux/pci-aspm.h
index ce68105..67cb3ae 100644
--- a/include/linux/pci-aspm.h
+++ b/include/linux/pci-aspm.h
@@ -26,6 +26,7 @@
extern void pcie_aspm_init_link_state(struct pci_dev *pdev);
extern void pcie_aspm_exit_link_state(struct pci_dev *pdev);
extern void pcie_aspm_pm_state_change(struct pci_dev *pdev);
+extern void pcie_aspm_powersave_config_link(struct pci_dev *pdev);
extern void pci_disable_link_state(struct pci_dev *pdev, int state);
extern void pcie_clear_aspm(void);
extern void pcie_no_aspm(void);
@@ -39,6 +40,9 @@ static inline void pcie_aspm_exit_link_state(struct pci_dev *pdev)
static inline void pcie_aspm_pm_state_change(struct pci_dev *pdev)
{
}
+static inline void pcie_aspm_powersave_config_link(struct pci_dev *pdev)
+{
+}
static inline void pci_disable_link_state(struct pci_dev *pdev, int state)
{
}
--
1.7.1.2


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