[PATCH] nvme-pci: Avoid to go into d3cold if device can't use npss.

[Kai-Heng Feng]

On Wed, May 26, 2021 at 10:28 PM Christoph Hellwig <hch at lst.de> wrote:
>
> On Wed, May 26, 2021 at 10:21:59PM +0800, Kai-Heng Feng wrote:
> > To be fair, resuming the NVMe from D3hot is much slower than keep it
> > at D0, which gives us a faster s2idle resume time. And now AMD also
> > requires s2idle on their latest laptops.
>
> We'd much prefer to use it, but due to the broken platforms we can't
> unfortunately.
>
> > And it's more like NVMe controllers don't respect PCI D3hot.
>
> What do you mean with that?

Originally, we found that under s2idle, most NVMe controllers caused
substantially more power if D3hot was used.
We were told by all the major NVMe vendors that D3hot is not
supported. It may also disable APST.
And that's the reason why we have the host-managed power control for s2idle.

IIRC only Samsung NVMes respect D3hot and keeps the power consumption low.

>
> > Because the NVMe continues to work after s2idle and the symbol is
> > rather subtle, so I suspect this is not platform or vendor specific.
> > Is it possible to disable DMA for HMB NVMe on suspend?
>
> Not in shipping products.  The NVMe technical working group is working
> on a way to do that, but it will take a while until that shows up in
> products.

Hmm, then what else can we do? Because D3hot isn't support by the
vendor, does it really stop HMB?

Kai-Heng