linux-kernel - Re: [RFC PATCH v2] xhci: Prevent runtime pm from autosuspending during initialization

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Message-ID: <20140228203200.GE3405@xanatos>
Date:	Fri, 28 Feb 2014 12:32:00 -0800
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	linux-usb@...r.kernel.org, david.a.cohen@...ux.intel.com,
	jianqiang.tang@...el.com, dan.j.williams@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] xhci: Prevent runtime pm from autosuspending
 during initialization

On Mon, Feb 24, 2014 at 12:44:46PM -0500, Alan Stern wrote:
> On Mon, 24 Feb 2014, Mathias Nyman wrote:
> 
> > xHCI driver has its own pci probe function that will call usb_hcd_pci_probe
> > to register its usb-2 bus, and then continue to manually register the
> > usb-3 bus. usb_hcd_pci_probe does a pm_runtime_put_noidle at the end and
> > might thus trigger a runtime suspend before the usb-3 bus is ready.
> > 
> > Prevent the runtime suspend by increasing the usage count in the
> > beginning of xhci_pci_probe, and decrease it once the usb-3 bus is
> > ready.
> > 
> > xhci-platform driver is not using usb_hcd_pci_probe to set up
> > busses and should not need to have it's usage count increased during probe.
> > 
> > Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
> > ---
> >  drivers/usb/host/xhci-pci.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
> > index 04f986d..ea7158b 100644
> > --- a/drivers/usb/host/xhci-pci.c
> > +++ b/drivers/usb/host/xhci-pci.c
> > @@ -190,6 +190,10 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
> >  	struct usb_hcd *hcd;
> >  
> >  	driver = (struct hc_driver *)id->driver_data;
> > +
> > +	/* Prevent USB-2 roothub runtime suspend until USB-3 is initialized. */
> > +	pm_runtime_get_noresume(&dev->dev);
> 
> Strictly speaking, this prevents the _controller_ from going into
> runtime suspend -- not the root hub.

Signed-off-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>

Mathias, want to fix this comment and queue this up to Greg?  It should
probably be marked for stable.

> Apart from nit about the comment,
> 
> Acked-by: Alan Stern <stern@...land.harvard.edu>
> 
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