Re: [PATCH] drm/amdgpu: always reset asic when going into suspend

[Daniel Drake <drake@endlessm.com>]

On Wed, Oct 16, 2019 at 2:43 AM Alex Deucher <alexdeucher@gmail.com> wrote:
> Is s2idle actually powering down the GPU?

My understanding is that s2idle (at a high level) just calls all
devices suspend routines and then puts the CPU into its deepest
running state.
So if there is something special to be done to power off the GPU, I
believe that amdgpu is responsible for making arrangements for that to
happen.
In this case the amdgpu code already does:

        pci_disable_device(dev->pdev);
        pci_set_power_state(dev->pdev, PCI_D3hot);

And the PCI layer will call through to any appropriate ACPI methods
related to that low power state.

> Do you see a difference in power usage?  I think you are just working around the fact that the
> GPU never actually gets powered down.

I ran a series of experiments.

Base setup: no UI running, ran "setterm -powersave 1; setterm -blank
1" and waited 1 minute for screen to turn off.
Base power usage in this state is 4.7W as reported by BAT0/power_now

1. Run amdgpu_device_suspend(ddev, true, true); before my change
--> Power usage increases to 6.1W

2. Run amdgpu_device_suspend(ddev, true, true); with my change applied
--> Power usage increases to 6.0W

3. Put amdgpu device in runtime suspend
--> Power usage increases to 6.2W

4. Try unmodified suspend path but d3cold instead of d3hot
--> Power usage increases to 6.1W

So, all of the suspend schemes actually increase the power usage by
roughly the same amount, reset or not, with and without my patch :/
Any ideas?

Thanks,
Daniel