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

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Date:	Mon, 24 Feb 2014 12:44:46 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Mathias Nyman <mathias.nyman@...ux.intel.com>
cc:	linux-usb@...r.kernel.org, <sarah.a.sharp@...ux.intel.com>,
	<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, 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.

> +
>  	/* Register the USB 2.0 roothub.
>  	 * FIXME: USB core must know to register the USB 2.0 roothub first.
>  	 * This is sort of silly, because we could just set the HCD driver flags
> @@ -199,7 +203,7 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  	retval = usb_hcd_pci_probe(dev, id);
>  
>  	if (retval)
> -		return retval;
> +		goto put_runtime_pm;
>  
>  	/* USB 2.0 roothub is stored in the PCI device now. */
>  	hcd = dev_get_drvdata(&dev->dev);
> @@ -228,12 +232,17 @@ static int xhci_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  	if (xhci->quirks & XHCI_LPM_SUPPORT)
>  		hcd_to_bus(xhci->shared_hcd)->root_hub->lpm_capable = 1;
>  
> +	/* USB-2 and USB-3 roothubs initialized, allow runtime pm suspend */
> +	pm_runtime_put_noidle(&dev->dev);
> +
>  	return 0;
>  
>  put_usb3_hcd:
>  	usb_put_hcd(xhci->shared_hcd);
>  dealloc_usb2_hcd:
>  	usb_hcd_pci_remove(dev);
> +put_runtime_pm:
> +	pm_runtime_put_noidle(&dev->dev);
>  	return retval;
>  }

Apart from nit about the comment,

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

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