linux-kernel - Re: [PATCH v3] PCI: enable ASPM configuration in PCIE POWERSAVE mode

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Date:	Thu, 17 Jul 2014 02:04:23 +0530
From:	vidya sagar <sagar.tv@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	matthew.garrett@...ula.com, rjw@...ysocki.net,
	nchumbalkar@...ovo.com, thierry.reding@...il.com,
	swarren@...dia.com, linux-pci@...r.kernel.org, kthota@...dia.com,
	linux-kernel@...r.kernel.org, vidyas@...dia.com
Subject: Re: [PATCH v3] PCI: enable ASPM configuration in PCIE POWERSAVE mode

On Thu, Jul 17, 2014 at 1:06 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Wed, Jul 16, 2014 at 03:33:42PM +0530, Vidya Sagar wrote:
>> From: Vidya Sagar <sagar.tv@...il.com>
>>
>> Commit 1a680b7c3258 ("PCI: PCIe links may not get configured for ASPM
>>  under POWERSAVE mode") moved pcie_aspm_powersave_config_link() out of
>> pci_raw_set_power_state() to pci_set_power_state() which would enable
>> ASPM. But, with Commit db288c9c5f9d ("PCI / PM: restore the original
>>  behavior of pci_set_power_state()"), which re-introduced the following check
>> ./drivers/pci/pci.c: pci_set_power_state()
>>
>> +     /* Check if we're already there */
>> +     if (dev->current_state == state)
>> +        return 0;
>>
>> in pci_set_power_state(), call to pcie_aspm_powersave_config_link() is never
>> made leaving ASPM broken.
>> Fix it by configuring links for ASPM in do_pci_enable_device() instead of
>> pci_set_power_state()
>>
>> Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
>> Signed-off-by: Vidya Sagar <sagar.tv@...il.com>
>
> I applied this to pci/misc for v3.17 with the following changelog:

Thanks,

>
> It would still make me feel better if Matthew and/or Rafael acked this.
>
>     PCI: Configure ASPM when enabling device
>
>     We can't do ASPM configuration at enumeration-time because enabling it
>     makes some defective hardware unresponsive, even if ASPM is disabled later
>     (see 41cd766b0659 ("PCI: Don't enable aspm before drivers have had a chance
>     to veto it").  Therefore, we have to do it after a driver claims the
>     device.
>
>     We previously configured ASPM in pci_set_power_state(), but that's not a
>     very good place because it's not really related to setting the PCI device
>     power state, and doing it there means:
>
>       - We incorrectly skipped ASPM config when setting a device that's
>         already in D0 to D0.
>
>       - We unnecessarily configured ASPM when setting a device to a low-power
>         state (the ASPM feature only applies when the device is in D0).
>
>       - We unnecessarily configured ASPM when called from a .resume() method
>         (ASPM configuration needs to be restored during resume, but I think
>         pci_restore_pcie_state() should already do this).
>
>     Move ASPM configuration from pci_set_power_state() to
>     do_pci_enable_device() so we do it when a driver enables a device.
>
>     [bhelgaas: changelog]
>     Link: https://bugzilla.kernel.org/show_bug.cgi?id=79621
>
> It would still make me feel better if Matthew and/or Rafael chimed in to
> make sure this is sane.
>
> Bjorn
>
>> ---
>> v3:
>> * Modified commit message
>>     removed single quotes around commit messages
>>     added Suggested-by line
>>
>> v2:
>> * Calling ASPM config code is moved from pci_set_power_state() to
>> * do_pci_enable_device()
>>
>>  drivers/pci/pci.c | 12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 1c8592b..81d49d3 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -839,12 +839,6 @@ 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;
>>  }
>> @@ -1195,12 +1189,18 @@ int __weak pcibios_enable_device(struct pci_dev *dev, int bars)
>>  static int do_pci_enable_device(struct pci_dev *dev, int bars)
>>  {
>>       int err;
>> +     struct pci_dev *bridge;
>>       u16 cmd;
>>       u8 pin;
>>
>>       err = pci_set_power_state(dev, PCI_D0);
>>       if (err < 0 && err != -EIO)
>>               return err;
>> +
>> +     bridge = pci_upstream_bridge(dev);
>> +     if (bridge)
>> +             pcie_aspm_powersave_config_link(bridge);
>> +
>>       err = pcibios_enable_device(dev, bars);
>>       if (err < 0)
>>               return err;
>> --
>> 1.8.1.5
>>
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