Re: [PATCH] PCI/PM: Put devices to low power state on shutdown

[Kai-Heng Feng]

On Fri, Sep 13, 2024 at 12:57 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> [+cc Rafael]
>
> On Thu, Sep 12, 2024 at 11:00:43AM +0800, Kai-Heng Feng wrote:
> > On Thu, Sep 12, 2024 at 3:05 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > > On Fri, Jul 12, 2024 at 02:24:11PM +0800, Kai-Heng Feng wrote:
> > > > Some laptops wake up after poweroff when HP Thunderbolt Dock G4 is
> > > > connected.
> > > >
> > > > The following error message can be found during shutdown:
> > > > pcieport 0000:00:1d.0: AER: Correctable error message received from 0000:09:04.0
> > > > pcieport 0000:09:04.0: PCIe Bus Error: severity=Correctable, type=Data Link Layer, (Receiver ID)
> > > > pcieport 0000:09:04.0:   device [8086:0b26] error status/mask=00000080/00002000
> > > > pcieport 0000:09:04.0:    [ 7] BadDLLP
> > > >
> > > > Calling aer_remove() during shutdown can quiesce the error message,
> > > > however the spurious wakeup still happens.
> > > >
> > > > The issue won't happen if the device is in D3 before system shutdown, so
> > > > putting device to low power state before shutdown to solve the issue.
> > > >
> > > > I don't have a sniffer so this is purely guesswork, however I believe
> > > > putting device to low power state it's the right thing to do.
> > >
> > > My objection here is that we don't have an explanation of why this
> > > should matter or a pointer to any spec language about this situation,
> > > so it feels a little bit random.
> >
> > I have the same feeling too. The PCIe spec doesn't specify what's the
> > correct power state for shutdown.
> > So we can only "logically" think the software should put devices to
> > low power state during shutdown.
> >
> > > I suppose the problem wouldn't happen if AER interrupts were disabled?
> > > We already do disable them in aer_suspend(), but maybe that's not used
> > > in the shutdown path?
> >
> > That was my first thought, so I modified pcie_port_shutdown_service()
> > to disable AER interrupt.
> > That approach didn't work though.
> >
> > > My understanding is that .shutdown() should turn off device interrupts
> > > and stop DMA.  So maybe we need an aer_shutdown() that disables
> > > interrupts?
> >
> > Logically we should do that. However that approach doesn't solve this issue.
>
> I'm not completely clear on the semantics of the .shutdown()
> interface.  The doc at
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/device/driver.h?id=v6.10#n73
> says "@shutdown: Called at shut-down time to quiesce the device"
>
> Turning off device interrupts and DMA *would* fit within the idea of
> quiescing the device.  Does that also include changing the device
> power state?  I dunno.  The power state isn't *mentioned* in the
> .shutdown() context, while it *is* mentioned for .suspend().

IMO putting a device to low power also qualifies as "quiesce the device".

>
> IIUC, this patch and commit log uses "shutdown" to refer to a
> system-wide *poweroff*, which is a different concept despite using the
> same "shutdown" name.

For ACPI based system, there are .suspend for S3/s2idle, .poweroff for
S4, and .shutdown for S5.
Unless we want to introduce a new callback for S5, I think the concept
is quite similar.

For DT based system, the OS should also perform the same thing, as
there's no firmware to cleanup the power state.

We can also move .shutdown to be part of pm_ops, but I don't think
it's necessary,

>
> So should the system poweroff procedure use .suspend()?  Should it use
> both .shutdown() and .suspend()?  I think it only uses .shutdown()
> today:
>
>   kernel_power_off
>     kernel_shutdown_prepare(SYSTEM_POWER_OFF)
>       device_shutdown
>         while (!list_empty(&devices_kset->list))
>           dev->bus->shutdown(dev)
>             pci_device_shutdown
>
> There are several driver .shutdown() methods that do things like this:
>
>   e1000_shutdown
>     if (system_state == SYSTEM_POWER_OFF)
>       pci_set_power_state(pdev, PCI_D3hot)
>
> Maybe that's the right thing and should be done by the PCI core, which
> is similar to what you propose here.  But I think it muddies the
> definition of .shutdown() a bit by mixing in power management stuff.

Do you think adding a new "low power state" callback to be called
after .shutdown a good idea?
That would make the concept of .shutdown different to .suspend and
.poweroff. I personally see .suspend, .poweroff and .shutdown the same
action but target different power states.

Kai-Heng

>
> > > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=219036
> > > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
> > > > ---
> > > >  drivers/pci/pci-driver.c | 8 ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > > index af2996d0d17f..4c6f66f3eb54 100644
> > > > --- a/drivers/pci/pci-driver.c
> > > > +++ b/drivers/pci/pci-driver.c
> > > > @@ -510,6 +510,14 @@ static void pci_device_shutdown(struct device *dev)
> > > >       if (drv && drv->shutdown)
> > > >               drv->shutdown(pci_dev);
> > > >
> > > > +     /*
> > > > +      * If driver already changed device's power state, it can mean the
> > > > +      * wakeup setting is in place, or a workaround is used. Hence keep it
> > > > +      * as is.
> > > > +      */
> > > > +     if (!kexec_in_progress && pci_dev->current_state == PCI_D0)
> > > > +             pci_prepare_to_sleep(pci_dev);
> > > > +
> > > >       /*
> > > >        * If this is a kexec reboot, turn off Bus Master bit on the
> > > >        * device to tell it to not continue to do DMA. Don't touch
> > > > --
> > > > 2.43.0
> > > >