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

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Date:	Wed, 16 Jul 2014 23:30:27 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Vidya Sagar <sagar.tv@...il.com>, matthew.garrett@...ula.com,
	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 Wednesday, July 16, 2014 01:36:37 PM Bjorn Helgaas 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:
> 
> 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.

I like the change, but I'm not sure whether or not it will work for everyone.

The only way to verify that seems to be to apply it, however.

Rafael

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