linux-kernel - Re: [PATCH v4 4/4] vfio/pci: Move the unused device into low power state with runtime PM

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Date:   Tue, 17 May 2022 14:55:39 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Abhishek Sahu <abhsahu@...dia.com>
Cc:     Cornelia Huck <cohuck@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        Kevin Tian <kevin.tian@...el.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] vfio/pci: Move the unused device into low power
 state with runtime PM

On Tue, 17 May 2022 14:42:56 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

> On Tue, 17 May 2022 15:32:19 +0530
> Abhishek Sahu <abhsahu@...dia.com> wrote:
> > 5. Since the runtime PM framework will provide the same functionality,
> >    so directly writing into PCI PM config register can be replaced with
> >    the use of runtime PM routines. Also, the use of runtime PM can help
> >    us in more power saving.
> > 
> >    In the systems which do not support D3cold,
> > 
> >    With the existing implementation:
> > 
> >    // PCI device
> >    # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> >    D3hot
> >    // upstream bridge
> >    # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> >    D0
> > 
> >    With runtime PM:
> > 
> >    // PCI device
> >    # cat /sys/bus/pci/devices/0000\:01\:00.0/power_state
> >    D3hot
> >    // upstream bridge
> >    # cat /sys/bus/pci/devices/0000\:00\:01.0/power_state
> >    D3hot  
> 
> I'm not able to reproduce these results.  Output below abridged:
> 
> # lspci -t
> -[0000:00]-+-00.0
>            +-01.0-[01]--+-00.0
>            |            \-00.1
> 
> # grep . /sys/bus/pci/devices/*/power_state
> /sys/bus/pci/devices/0000:00:01.0/power_state:D0
> /sys/bus/pci/devices/0000:01:00.0/power_state:D3hot
> /sys/bus/pci/devices/0000:01:00.1/power_state:D3hot
> 
> # lspci -ks $DEV
> 00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v2/3rd Gen Core processor PCI Express Root Port (rev 09)
> 	Kernel driver in use: pcieport
> 01:00.0 VGA compatible controller: NVIDIA Corporation GM107 [GeForce GTX 750] (rev a2)
> 	Subsystem: eVga.com. Corp. Device 2753
> 	Kernel driver in use: vfio-pci
> 01:00.1 Audio device: NVIDIA Corporation GM107 High Definition Audio Controller [GeForce 940MX] (rev a1)
> 	Subsystem: eVga.com. Corp. Device 2753
> 	Kernel driver in use: vfio-pci
> 	Kernel modules: snd_hda_intel
> 
> Any debugging suggestions?  Thanks,

Nevermind, I see a whole bunch of reasons in pci_bridge_d3_possible()
that runtime-pm wouldn't support D3hot on this bridge/system.  Thanks,

Alex