linux-kernel - Re: [PATCH v1] PCI: enable ASPM configuration in PCIE POWERSAVE mode

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Message-ID: <20140705190203.GE28871@google.com>
Date:	Sat, 5 Jul 2014 13:02:03 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Vidya Sagar <vidyas@...dia.com>
Cc:	nagananda.chumbalkar@...com, thierry.reding@...il.com,
	swarren@...dia.com, kthota@...dia.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Matthew Garrett <matthew.garrett@...ula.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v1] PCI: enable ASPM configuration in PCIE POWERSAVE mode

[+cc Rafael]

On Sat, Jul 05, 2014 at 12:57:36PM -0600, Bjorn Helgaas wrote:
> [+cc Matthew]
> 
> On Tue, Jul 01, 2014 at 12:46:18PM +0530, Vidya Sagar wrote:
> > commit 1a680b7c 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 db288c9c, 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 not returning from when the above condition is true, rather, jump to
> > ASPM configuration code and exit from there eventually.
> 
> Rafael, Matthew, any comments?  We have vacillated on this before and
> the web is already pretty tangled.
> 
> Vidya, can you give more details about the bug fixed by this change?
> What's the scenario?  Are we resuming and the device is powered up but
> ASPM isn't enabled?  Maybe you could collect more details in a
> http://bugzilla.kernel.org report?
> 
> > Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> > ---
> >  drivers/pci/pci.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 1c8592b..ded24c4 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -804,7 +804,7 @@ EXPORT_SYMBOL_GPL(__pci_complete_power_transition);
> >   */
> >  int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
> >  {
> > -	int error;
> > +	int error = 0;
> >  
> >  	/* bound the state we're entering */
> >  	if (state > PCI_D3cold)
> > @@ -821,7 +821,7 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
> >  
> >  	/* Check if we're already there */
> >  	if (dev->current_state == state)
> > -		return 0;
> > +		goto config_aspm;
> >  
> >  	__pci_start_power_transition(dev, state);
> >  
> > @@ -839,6 +839,8 @@ int pci_set_power_state(struct pci_dev *dev, pci_power_t state)
> >  
> >  	if (!__pci_complete_power_transition(dev, state))
> >  		error = 0;
> > +
> > +config_aspm:
> >  	/*
> >  	 * When aspm_policy is "powersave" this call ensures
> >  	 * that ASPM is configured.
> > -- 
> > 1.8.1.5
> > 
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