linux-kernel - Re: [PATCH v2 1/2] USB: core: Disable remote wakeup for freeze/quiesce

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Date:   Wed, 20 Apr 2022 12:30:16 -0700
From:   Evan Green <evgreen@...omium.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Rajat Jain <rajatja@...omium.org>,
        Razvan Heghedus <heghedus.razvan@...il.com>,
        Wei Ming Chen <jj251510319013@...il.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 1/2] USB: core: Disable remote wakeup for freeze/quiesce

On Tue, Apr 19, 2022 at 7:41 AM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Mon, Apr 18, 2022 at 02:00:45PM -0700, Evan Green wrote:
> > The PM_EVENT_FREEZE and PM_EVENT_QUIESCE messages should cause the
> > device to stop generating interrupts. USB core was previously allowing
> > devices that were already runtime suspended to keep remote wakeup
> > enabled if they had gone down that way. This violates the contract with
> > pm, and can potentially cause MSI interrupts to be lost.
> >
> > Change that so that if a device is runtime suspended with remote wakeups
> > enabled, it will be resumed to ensure remote wakeup is always disabled
> > across a freeze.
> >
> > Signed-off-by: Evan Green <evgreen@...omium.org>
> > ---
> >
> > (no changes since v1)
> >
> >  drivers/usb/core/driver.c | 20 +++++++++-----------
> >  1 file changed, 9 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> > index 355ed33a21792b..93c8cf66adccec 100644
> > --- a/drivers/usb/core/driver.c
> > +++ b/drivers/usb/core/driver.c
> > @@ -1533,20 +1533,18 @@ static void choose_wakeup(struct usb_device *udev, pm_message_t msg)
> >  {
> >       int     w;
> >
> > -     /* Remote wakeup is needed only when we actually go to sleep.
> > -      * For things like FREEZE and QUIESCE, if the device is already
> > -      * autosuspended then its current wakeup setting is okay.
> > +     /* For FREEZE/QUIESCE, disable remote wakeups so no interrupts get generated
> > +      * by the device.
>
> You mean "by the host controller".  USB devices don't generate
> interrupts; they generate wakeup requests (which can cause a host
> controller to generate an interrupt).

Right, I guess I mean "at the behest of the device". I could probably
just delete "by the device", since the goal of the comment is simply
to highlight that we're trying to kill interrupts, and describing
their provenance isn't as relevant.

>
> >        */
> >       if (msg.event == PM_EVENT_FREEZE || msg.event == PM_EVENT_QUIESCE) {
> > -             if (udev->state != USB_STATE_SUSPENDED)
> > -                     udev->do_remote_wakeup = 0;
> > -             return;
> > -     }
> > +             w = 0;
> >
> > -     /* Enable remote wakeup if it is allowed, even if no interface drivers
> > -      * actually want it.
> > -      */
> > -     w = device_may_wakeup(&udev->dev);
> > +     } else {
> > +             /* Enable remote wakeup if it is allowed, even if no interface drivers
> > +              * actually want it.
> > +              */
> > +             w = device_may_wakeup(&udev->dev);
> > +     }
> >
> >       /* If the device is autosuspended with the wrong wakeup setting,
> >        * autoresume now so the setting can be changed.
> > --
>
> I would prefer it if you reformatted the comments to agree with the
> current style:
>
>         /*
>          * Blah blah blah
>          */
>
> and to avoid line wrap beyond 80 columns.  Apart from that:

Sure, I can fix these up, add your tags, and repost.

>
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Thanks!

>
> Alan Stern