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

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Message-ID: <20250103072805.GB28920@lst.de>
Date: Fri, 3 Jan 2025 08:28:05 +0100
From: Christoph Hellwig <hch@....de>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Christoph Hellwig <hch@....de>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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 Fri, Dec 20, 2024 at 04:15:21PM +0100, Konrad Dybcio wrote:
> The Qualcomm platform (or class of platforms) we're looking at with this
> specific issue requires PCIe (implying NVMe) shutdown for S2RAM.
> 
> The S2RAM entry mechanism is unfortunately misrepresented as an S2Idle
> state by Linux as of today, and I'm trying really hard to convince some
> folks to let me describe it correctly, with little success so far..

Well, not advertizing the right mechanism isn't going to cause havoc
to any scheme.

> That is the real underlying issue and once/if it's solved, this patch
> will not be necessary.

Well, maybe this thread gave good enough fodder to finally fix it?

> 
> > 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.
> 
> In our case the plug is only pulled in S2RAM, otherwise the best we can
> do is just turn off the devices individually to decrease the overall
> power draw

FYI, going to D3 for S2RAM seems perfectly reasonable from the NVMe POV.