linux-kernel - Re: [PATCH 2/6] USB / PCI / PM: Allow the PCI core to do the resume cleanup

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Date:   Fri, 09 Jun 2017 01:01:45 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Linux USB <linux-usb@...r.kernel.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Felipe Balbi <balbi@...nel.org>,
        Mario Limonciello <mario_limonciello@...l.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Hans De Goede <hdegoede@...hat.com>
Subject: Re: [PATCH 2/6] USB / PCI / PM: Allow the PCI core to do the resume cleanup

On Thursday, June 08, 2017 11:24:55 AM Alan Stern wrote:
> On Thu, 8 Jun 2017, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > 
> > hcd_pci_resume_noirq() used as a universal _resume_noirq handler for
> > PCI USB controllers calls pci_back_from_sleep() which is unnecessary
> > and may become problematic.
> > 
> > It is unnecessary, because the PCI bus type carries out post-suspend
> > cleanup of all PCI devices during resume and that covers all things
> > done by the pci_back_from_sleep().  There is no reason why USB cannot
> > follow all of the other PCI devices in that respect.
> > 
> > It will become problematic after subsequent changes that make it
> > possible to go back to sleep again after executing dpm_resume_noirq()
> > if no valid system wakeup events have been detected at that point.
> > Namely, calling pci_back_from_sleep() at the _resume_noirq stage
> > will cause the wakeup status of the devices in question to be cleared
> > and if any of them has triggered system wakeup, that event may be
> > missed then.
> > 
> > For the above reasons, drop the pci_back_from_sleep() invocation
> > from hcd_pci_resume_noirq().
> > 
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >  drivers/usb/core/hcd-pci.c |    7 +------
> >  1 file changed, 1 insertion(+), 6 deletions(-)
> > 
> > Index: linux-pm/drivers/usb/core/hcd-pci.c
> > ===================================================================
> > --- linux-pm.orig/drivers/usb/core/hcd-pci.c
> > +++ linux-pm/drivers/usb/core/hcd-pci.c
> > @@ -584,12 +584,7 @@ static int hcd_pci_suspend_noirq(struct
> >  
> >  static int hcd_pci_resume_noirq(struct device *dev)
> >  {
> > -	struct pci_dev		*pci_dev = to_pci_dev(dev);
> > -
> > -	powermac_set_asic(pci_dev, 1);
> > -
> > -	/* Go back to D0 and disable remote wakeup */
> > -	pci_back_from_sleep(pci_dev);
> > +	powermac_set_asic(to_pci_dev(dev), 1);
> >  	return 0;
> >  }
> 
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Thanks!