linux-kernel - Re: [RFC][PATCH v2]: PCI: PCIe links may not get configured for ASPM under POWERSAVE mode

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Date:	Fri, 18 Mar 2011 14:29:16 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Naga Chumbalkar <nagananda.chumbalkar@...com>
CC:	jbarnes@...tuousgeek.org, rjw@...k.pl, mjg59@...f.ucam.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RFC][PATCH v2]: PCI: PCIe links may not get configured for ASPM
 under POWERSAVE mode

(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	: 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 POWERSAVE is no longer valid.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. 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?

Regards,
Kenji Kaneshige

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