linux-kernel - Re: [PATCH] mfd: dln2: add suspend/resume functionality

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Message-ID: <20141205120610.GG11445@localhost>
Date:	Fri, 5 Dec 2014 13:06:10 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	Johan Hovold <johan@...nel.org>, Lee Jones <lee.jones@...aro.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mfd: dln2: add suspend/resume functionality

On Fri, Dec 05, 2014 at 01:51:17PM +0200, Octavian Purdila wrote:
> On Fri, Dec 5, 2014 at 12:17 PM, Johan Hovold <johan@...nel.org> wrote:
> > On Thu, Nov 27, 2014 at 01:57:14PM +0200, Octavian Purdila wrote:
> >
> >> @@ -753,11 +759,42 @@ static const struct usb_device_id dln2_table[] = {
> >>
> >>  MODULE_DEVICE_TABLE(usb, dln2_table);
> >
> > Place the new callbacks above the device id table.
> >
> >> +static int dln2_suspend(struct usb_interface *iface, pm_message_t message)
> >> +{
> >> +     struct dln2_dev *dln2 = usb_get_intfdata(iface);
> >> +
> >> +     dln2_stop(dln2);
> >
> > You should also stop the reads urbs here.
> 
> Do you mean usb_kill_urb()? I thought that was not necessary unless
> the device is reset. However, going throught
> Documentation/usb/power-management.txt again looks like it must be
> done in suspend.

Yes, you should kill them explicitly. Any outstanding urbs will be
killed by usb core if you fail to do this.

> >> +     return 0;
> >> +}
> >> +
> >> +static int dln2_resume(struct usb_interface *iface)
> >> +{
> >> +     struct dln2_dev *dln2 = usb_get_intfdata(iface);
> >> +
> >> +     dln2->disconnect = false;
> >
> > And surely you need to resubmit the read urbs in resume, or you will
> > never receive any more data.
> >
> > How did you test this patch?
> >
> 
> The resume cb is not called in my setup (kvm), only reset_resume. 

Please make sure to test your patches on proper hardware.

> But I assume since the port is not reset when resume is called the
> URBs are still queued.

No, they will have been killed by usb core even if you forget to do it,
so this would prevent any further reads.

> >> +     return 0;
> >> +}
> >> +
> >> +static int dln2_reset_resume(struct usb_interface *iface)
> >> +{
> >> +     struct dln2_dev *dln2 = usb_get_intfdata(iface);
> >> +     int ret;
> >> +
> >> +     dln2_free_rx_urbs(dln2);
> >> +     ret = dln2_setup_rx_urbs(dln2, iface->cur_altsetting);
> >
> > This doesn't make much sense. Why would you ever want to reallocate the
> > urbs and their buffers here?
> >
> > If the device does not lose its state as you claim, then all you need to
> > do is to resubmit the read urbs (as in resume).
> >
> The device itself does not lose state as it does not lose power and
> does not react to USB port reset AFAICS (e.g. GPIO settings are
> preserved). However the USB port is reset and I assumed I must
> reallocate the URBs.

You don't and should not.

> I just found out that usb-serial uses usb_poisoin_urb and
> usb_unpoison_urb for suspend/resume and this two looks like just what
> I need.

Why do you think so?

> Should I use that instead?

No.

Johan
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