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

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Message-ID: <CAJZ5v0g8CdGgWA7e6TXpUjYNkU1zX46Rz3ELiun42MayoN0osA@mail.gmail.com>
Date: Mon, 16 Dec 2024 17:42:30 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, 
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Bjorn Helgaas <helgaas@...nel.org>, kbusch@...nel.org, 
	axboe@...nel.dk, sagi@...mberg.me, linux-nvme@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, andersson@...nel.org, 
	konradybcio@...nel.org, Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: Shutdown the device if D3Cold is allowed by the user

On Mon, Dec 16, 2024 at 5:23 PM Christoph Hellwig <hch@....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.