linux-kernel - Re: [PATCH] PCI / PM: Don't runtime suspend when device only supports wakeup from D0

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Message-ID: <20190522181157.GC79339@google.com>
Date:   Wed, 22 May 2019 13:11:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kai Heng Feng <kai.heng.feng@...onical.com>
Cc:     Rafael Wysocki <rafael.j.wysocki@...el.com>,
        linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] PCI / PM: Don't runtime suspend when device only
 supports wakeup from D0

On Wed, May 22, 2019 at 11:46:25PM +0800, Kai Heng Feng wrote:
> > On May 22, 2019, at 9:48 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > On Wed, May 22, 2019 at 11:42:14AM +0800, Kai Heng Feng wrote:
> >> at 6:23 AM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> >>> On Wed, May 22, 2019 at 12:31:04AM +0800, Kai-Heng Feng wrote:
> >>>> There's an xHC device that doesn't wake when a USB device gets plugged
> >>>> to its USB port. The driver's own runtime suspend callback was called,
> >>>> PME signaling was enabled, but it stays at PCI D0.

> > ...
> > And I guess this patch basically means we wouldn't call the driver's
> > suspend callback if we're merely going to stay at D0, so the driver
> > would have no idea anything happened.  That might match
> > Documentation/power/pci.txt better, because it suggests that the
> > suspend callback is related to putting a device in a low-power state,
> > and D0 is not a low-power state.
> 
> Yes, the patch is to let the device stay at D0 and don’t run driver’s own
> runtime suspend routine.
> 
> I guess I’ll just proceed to send a V2 with updated commit message?

Now that I understand what "runtime suspended to D0" means, help me
understand what's actually wrong.

The PCI core apparently *does* enable PME when we "suspend to D0".
But somehow calling the xHCI runtime suspend callback makes the driver
unable to notice when the PME is signaled?

Bjorn