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

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Date:   Tue, 25 May 2021 09:44:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Koba Ko <koba.ko@...onical.com>
Cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Henrik Juul Hansen <hjhansen2020@...il.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: Avoid to go into d3cold if device can't use
 npss.

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?