linux-kernel - Re: [PATCH v2 2/8] USB / PCI / PM: Allow the PCI core to do the resume cleanup

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Date:   Tue, 13 Jun 2017 13:14:27 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Greg KH <greg@...ah.com>
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>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v2 2/8] USB / PCI / PM: Allow the PCI core to do the resume cleanup

On Tuesday, June 13, 2017 10:52:52 AM Greg KH wrote:
> On Mon, Jun 12, 2017 at 10:49:40PM +0200, 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>
> > Acked-by: Alan Stern <stern@...land.harvard.edu>
> 
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks!