Re: [PATCH] nvme-pci: Use non-operational power state instead of D3 on Suspend-to-Idle

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, May 9, 2019 at 9:33 PM Keith Busch <kbusch@kernel.org> wrote:
>
> On Thu, May 09, 2019 at 06:57:34PM +0000, Mario.Limonciello@dell.com wrote:
> > No, current Windows versions don't transition to D3 with inbox NVME driver.
> > You're correct, it's explicit state transitions even if APST was enabled
> > (as this patch is currently doing as well).
>
> The proposed patch does too much, and your resume latency will be worse
> off for doing an unnecessary controller reset.
>
> The following should be all that's needed if the device is spec
> compliant. The resume part isn't necessary if npss is non-operational, but
> we're not saving that info, and it shouldn't hurt to be explicit anyway.
>
> I don't have any PS capable devices, so this is just compile tested.
>
> ---
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 6265d9225ec8..ce8b9bc949b9 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -1132,6 +1132,22 @@ static int nvme_set_features(struct nvme_ctrl *dev, unsigned fid, unsigned dword
>         return ret;
>  }
>
> +int nvme_set_power(struct nvme_ctrl *ctrl, unsigned npss)
> +{
> +       int ret;
> +
> +       mutex_lock(&ctrl->scan_lock);
> +       nvme_start_freeze(ctrl);
> +       nvme_wait_freeze(ctrl);
> +       ret = nvme_set_features(ctrl, NVME_FEAT_POWER_MGMT, npss, NULL, 0,
> +                               NULL);
> +       nvme_unfreeze(ctrl);
> +       mutex_unlock(&ctrl->scan_lock);
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(nvme_set_power);
> +
>  int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count)
>  {
>         u32 q_count = (*count - 1) | ((*count - 1) << 16);
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index 527d64545023..f2be6aad9804 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -459,6 +459,7 @@ int __nvme_submit_sync_cmd(struct request_queue *q, struct nvme_command *cmd,
>                 unsigned timeout, int qid, int at_head,
>                 blk_mq_req_flags_t flags, bool poll);
>  int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count);
> +int nvme_set_power(struct nvme_ctrl *ctrl, unsigned npss);
>  void nvme_stop_keep_alive(struct nvme_ctrl *ctrl);
>  int nvme_reset_ctrl(struct nvme_ctrl *ctrl);
>  int nvme_reset_ctrl_sync(struct nvme_ctrl *ctrl);
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index a90cf5d63aac..2c4154cb4e79 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -18,6 +18,7 @@
>  #include <linux/mutex.h>
>  #include <linux/once.h>
>  #include <linux/pci.h>
> +#include <linux/suspend.h>
>  #include <linux/t10-pi.h>
>  #include <linux/types.h>
>  #include <linux/io-64-nonatomic-lo-hi.h>
> @@ -2851,6 +2852,8 @@ static int nvme_suspend(struct device *dev)
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct nvme_dev *ndev = pci_get_drvdata(pdev);
>
> +       if (!pm_suspend_via_firmware())
> +               return nvme_set_power(&ndev->ctrl, ndev->ctrl.npss);

You probably want to call pci_save_state(pdev) in the branch above to
prevent pci_pm_suspend_noirq() from calling pci_prepare_to_sleep()
going forward, so I would write this routine as

if (pm_suspend_via_firmware()) {
        nvme_dev_disable(ndev, true);
        return 0;
}

pci_save_state(pdev)
return nvme_set_power(&ndev->ctrl, ndev->ctrl.npss);

>         nvme_dev_disable(ndev, true);
>         return 0;
>  }
> @@ -2860,6 +2863,8 @@ static int nvme_resume(struct device *dev)
>         struct pci_dev *pdev = to_pci_dev(dev);
>         struct nvme_dev *ndev = pci_get_drvdata(pdev);
>
> +       if (!pm_suspend_via_firmware())
> +               return nvme_set_power(&ndev->ctrl, 0);
>         nvme_reset_ctrl(&ndev->ctrl);
>         return 0;
>  }

The rest of the patch LGTM.