linux-kernel - Re: [PATCH] nvme-pci: Save PCI state before putting drive into deepest state

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Message-ID: <9775216.kg7gRTdaXr@kreacher>
Date:   Wed, 18 Sep 2019 23:42:44 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Mario Limonciello <mario.limonciello@...l.com>,
        Keith Busch <kbusch@...nel.org>
Cc:     Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Ryan Hong <Ryan.Hong@...l.com>, Crag Wang <Crag.Wang@...l.com>,
        sjg@...gle.com, Jared Dominguez <jared.dominguez@...l.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] nvme-pci: Save PCI state before putting drive into deepest state

On Wednesday, September 18, 2019 11:31:19 PM CEST Rafael J. Wysocki wrote:
> 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@...l.com>
> > ---
> >  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.

BTW, doing nvme_dev_disable() before nvme_unfreeze() looks odd to me.

Maybe it would be better to do "unfreeze" and then "disable" in this case?

> 
> >  	}
> > -	/*
> > -	 * 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;
> > 
> 
> 
> 
> 
>