Re: [PATCH] nvme-pci: Shutdown the device if D3Cold is allowed by the user

Rafael J. Wysocki
2024-12-16T16:42:42Z

On Mon, Dec 16, 2024 at 5:23 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Sat, Dec 14, 2024 at 12:00:23PM +0530, Manivannan Sadhasivam wrote:
> > We need a PM core API that tells the device drivers when it is safe to powerdown
> > the devices. The usecase here is with PCIe based NVMe devices but the problem is
> > applicable to other devices as well.
>
> Maybe I'm misunderstanding things, but I think the important part is
> to indicate when a suspend actually MUST put the device into D3. Because
> doing that should always be safe, but not always optimal.

I'm not aware of any cases when a device must be put into D3cold
(which I think is what you mean) during system-wide suspend.

Suspend-to-idle on x86 doesn't require this, at least not for
correctness. I don't think any platforms using DT require it either.

In theory, ACPI S3 or hibernation may request that, but I've never
seen it happen in practice.

Suspend-to-idle on x86 may want devices to end up in specific power
states in order to be able to switch the entire platform into a deep
energy-saving mode, but that's never been D3cold so far.