Re: [RFC][PATCH v2]: PCI: PCIe links may not get configured for ASPMunder POWERSAVE mode

From: Kenji Kaneshige
Date: Fri Mar 18 2011 - 01:29:46 EST

(2011/03/18 13:21), Naga Chumbalkar wrote:
v2 -> v1:
. Kept the logic in pci_raw_set_power_state
. Changed the ASPM enabling logic
. Modified the text that describes the problem

v1 :

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POWERSAVE is no longer valid.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. This makes the
equality check (below) become true, so pcie_aspm_pm_state_change() never
gets called.
./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;

So OSPM doesnn't configure the PCIe links for ASPM.

The patch below does the following:
At the end of each Root Bridge scan make a call to configure ASPM when the
ASPM policy is set to "powersave" mode. Note that if a previous pass had
completed the configuration for all devices under that Bridge then the
configuration will not take place again because pcie_config_aspm_link()
checks to see if the link is already in the requested state.
We won't reconfigure ASPM when _OSC control is not granted.

Which _OSC controls do we need for configuring ASPM?

Kenji Kaneshige

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