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

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Message-ID: <20190917212414.GB39848@C02WT3WMHTD6.wdl.wdc.com>
Date:   Tue, 17 Sep 2019 15:24:14 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Mario Limonciello <mario.limonciello@...l.com>
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>
Subject: Re: [PATCH] nvme-pci: Save PCI state before putting drive into
 deepest state

On Wed, Sep 11, 2019 at 06:42:33PM -0500, 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.
>
> 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)
>  		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);
>  unfreeze:
>  	nvme_unfreeze(ctrl);
>  	return ret;

In the event that something else fails after the point you've saved
the state, we need to fallback to the behavior for when the driver
doesn't save the state, right?