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

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Message-ID: <95f25457-c1dd-4125-8f0d-46d87a1d5356@oss.qualcomm.com>
Date: Fri, 3 Jan 2025 12:48:55 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Christoph Hellwig <hch@....de>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
        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 3.01.2025 8:28 AM, Christoph Hellwig wrote:
> 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?

Oh I'd love to..

But my changes are getting rejected over philosophical FW design
disagreements, it seems.

Konrad

> 
>>
>>> 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.
>