[Bug] nvme blocks PC10 since v5.15 - bisected

[Keith Busch]

On Fri, Jan 21, 2022 at 08:00:49PM +0100, Rafael J. Wysocki wrote:
> Hi Keith,
> 
> It is reported that the following commit
> 
> commit e5ad96f388b765fe6b52f64f37e910c0ba4f3de7
> Author: Keith Busch <kbusch at kernel.org>
> Date:   Tue Jul 27 09:40:44 2021 -0700
> 
>    nvme-pci: disable hmb on idle suspend
> 
>    An idle suspend may or may not disable host memory access from devices
>    placed in low power mode. Either way, it should always be safe to
>    disable the host memory buffer prior to entering the low power mode, and
>    this should also always be faster than a full device shutdown.
> 
>    Signed-off-by: Keith Busch <kbusch at kernel.org>
>    Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
>    Signed-off-by: Christoph Hellwig <hch at lst.de>
> 
> is the source of a serious power regression occurring since 5.15
> (please see https://bugzilla.kernel.org/show_bug.cgi?id=215467).
> 
> After this commit, the SoC on the affected system cannot enter
> C-states deeper than PC2 while suspended to idle which basically
> defeats the purpose of suspending.
> 
> What may be happening is that nvme_disable_prepare_reset() that is not
> called any more in the ndev->nr_host_mem_descs case somehow causes the
> LTR of the device to change to "no requirement" which allows deeper
> C-states to be entered.
> 
> Can you have a look at this, please?

I thought platforms that wanted full device shutdown  behaviour would
always set acpi_storage_d3. Is that not happening here?