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

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Message-ID: <20241216164830.36lpu6gfnapsdar4@thinkpad>
Date: Mon, 16 Dec 2024 22:18:30 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Christoph Hellwig <hch@....de>, 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 05:42:30PM +0100, Rafael J. Wysocki wrote:
> 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.
> 

On suspend-to-idle, yes D3Cold doesn't make sense, but on suspend-to-ram it is
pretty much required. That applies to DT as well.

- Mani

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