RE: [PATCH] nvme-pci: Save PCI state before putting drive into deepest state

[Mario.Limonciello]

> -----Original Message-----
> From: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Sent: Wednesday, September 18, 2019 4:31 PM
> To: Limonciello, Mario
> Cc: Keith Busch; Jens Axboe; Christoph Hellwig; Sagi Grimberg; linux-
> nvme@xxxxxxxxxxxxxxxxxxx; LKML; Hong, Ryan; Wang, Crag; sjg@xxxxxxxxxx;
> Dominguez, Jared; Linux PCI; Linux PM
> Subject: Re: [PATCH] nvme-pci: Save PCI state before putting drive into deepest
> state
> 
> 
> [EXTERNAL EMAIL]
> 
> On Thursday, September 12, 2019 1:42:33 AM CEST Mario Limonciello wrote:
> > The action of saving the PCI state will cause numerous PCI configuration
> > space reads which depending upon the vendor implementation may cause
> > the drive to exit the deepest NVMe state.
> >
> > In these cases ASPM will typically resolve the PCIe link state and APST
> > may resolve the NVMe power state.  However it has also been observed
> > that this register access after quiesced will cause PC10 failure
> > on some device combinations.
> >
> > To resolve this, move the PCI state saving to before SetFeatures has been
> > called.  This has been proven to resolve the issue across a 5000 sample
> > test on previously failing disk/system combinations.
> 
> This sounds reasonable to me, but it would be nice to CC that to linux-pm
> and/or linux-pci too.
> 
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxxx>
> > ---
> >  drivers/nvme/host/pci.c | 13 +++++++------
> >  1 file changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > index 732d5b6..9b3fed4 100644
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -2894,6 +2894,13 @@ static int nvme_suspend(struct device *dev)
> >  	if (ret < 0)
> >  		goto unfreeze;
> >
> > +	/*
> > +	 * A saved state prevents pci pm from generically controlling the
> > +	 * device's power. If we're using protocol specific settings, we don't
> > +	 * want pci interfering.
> > +	 */
> > +	pci_save_state(pdev);
> > +
> >  	ret = nvme_set_power_state(ctrl, ctrl->npss);
> >  	if (ret < 0)
> >  		goto unfreeze;
> > @@ -2908,12 +2915,6 @@ static int nvme_suspend(struct device *dev)
> 
> This is the case in which the PCI layer is expected to put the device into
> D3, so you need
> 
> pdev->state_saved = 0;
> 
> at this point, because you have saved the config space already.
> 
> >  		ret = 0;
> >  		goto unfreeze;
> 
> And here you don't need to jump to "unfreeze" any more.
> 
> >  	}
> > -	/*
> > -	 * A saved state prevents pci pm from generically controlling the
> > -	 * device's power. If we're using protocol specific settings, we don't
> > -	 * want pci interfering.
> > -	 */
> > -	pci_save_state(pdev);
> >  unfreeze:
> >  	nvme_unfreeze(ctrl);
> >  	return ret;
> >
> 
> 
> 

Thanks, I actually followed up with something along that line in a v2 sent out
today.  My apology you weren't in CC, but here is a weblink to it.
http://lists.infradead.org/pipermail/linux-nvme/2019-September/027251.html