RE: [PATCH] nvme-pci: set some AMD PCIe downstream storage device to D3 for s2idle

[Public]

quoted

For context, here's the summary from my understanding:

We (linux-nvme) received a bug report that a platform fails to resume
after idle suspend due to mismatched behavior with the nvme driver.

When suspending, the nvme driver checks pm_suspend_via_firmware(). If
false, the driver assumes platform firmware will not alter our device's
power state after the kernel completes its suspend process.

But this platform's SMU firmware will remove power from the device.

How exactly does it do that?

It's running as a result of a platform driver notifying it to run (amd-pmc).

In particular, how does it get a chance to run?

quoted

Since the driver believed that wouldn't happen, the driver did not
prepare the device for this powerloss event.

It seems that the kernel's assumptions around pm_suspend_via_firmware()
and pm_suspend_no_platform() may not accurately reflect what the
platform's firmware actually does.

Note that this is not about whether or not AML will remove power from devices.

It is about passing control entirely to the platform firmware at the end of the
suspend transition.

If instead the kernel executes AML that happens to remove power from some
devices, that is a totally different case which should not be confused with
the above.

quoted

I do not know of a better way to detect if the platform will remove power,
so I'm looking at quirks to suppress PM_SUSPEND_FLAG_NO_PLATFORM for
this platform. I'm hoping there's a better option, though :)

Honestly, I'm not sure about the clear understanding of what's really going on
here.

We'll discuss internally and come back with a different proposal.
Thanks all for your feedback.
_______________________________________________
Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme