[PATCH] nvme-pci: Avoid to go into d3cold if device can't use npss.

[Christoph Hellwig]

On Thu, May 20, 2021 at 11:33:15AM +0800, Koba Ko wrote:
> After resume, host can't change power state of the closed controller
> from D3cold to D0.

Why?

> For these devices, just avoid to go deeper than d3hot.

What are "these devices"?

> @@ -2958,6 +2959,15 @@ static int nvme_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  
>  	dev_info(dev->ctrl.device, "pci function %s\n", dev_name(&pdev->dev));
>  
> +	if (pm_suspend_via_firmware() || !dev->ctrl.npss ||
> +	    !pcie_aspm_enabled(pdev) ||
> +	    dev->nr_host_mem_descs ||
> +	    (dev->ctrl.quirks & NVME_QUIRK_SIMPLE_SUSPEND)) {

Before we start open coding this in even more places we really want a
little helper function for these checks, which should be accomodated with
the comment near the existing copy of the checks.

> +		pdev->d3cold_allowed = false;
> +		pci_d3cold_disable(pdev);
> +		pm_runtime_resume(&pdev->dev);

Why do we need to both set d3cold_allowed and call pci_d3cold_disable?

What is the pm_runtime_resume doing here?