Re: [PATCH 1/1] usb: core: lpm: set lpm_capable for root hub device

[Lu, Baolu]

On 06/13/2015 01:43 AM, Alan Stern wrote:
> On Fri, 12 Jun 2015, Lu Baolu wrote:
>
> > Commit 25cd2882e2fc ("usb/xhci: Change how we indicate a host supports
> > Link PM.") removed the code to set lpm_capable for USB 3.0 super-speed
> > root hub. The intention of that change was to avoid touching usb core
> > internal field, a.k.a. lpm_capable, and let usb core to set it by
> > checking U1 and U2 exit latency values in the descriptor.
> >
> > Usb core checks and sets lpm_capable in hub_port_init(). Unfortunately,
> > root hub is a special usb device as it has no parent. Hub_port_init()
> > will never be called for a root hub device. That means lpm_capable will
> > by no means be set for the root hub. As the result, lpm isn't functional
> > at all in Linux kernel.
> >
> > This patch add the code to check and set lpm_capable when registering a
> > root hub device. It could be back-ported to kernels as old as v3.15,
> > that contains the Commit 25cd2882e2fc ("usb/xhci: Change how we indicate
> > a host supports Link PM.").
> >
> > Cc: stable@xxxxxxxxxxxxxxx # 3.15
> > Reported-by: Kevin Strasser <kevin.strasser@xxxxxxxxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/usb/core/hcd.c | 6 ++++++
> >   drivers/usb/core/hub.c | 2 +-
> >   drivers/usb/core/usb.h | 1 +
> >   3 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > index 45a915c..48b208d 100644
> > --- a/drivers/usb/core/hcd.c
> > +++ b/drivers/usb/core/hcd.c
> > @@ -1032,6 +1032,12 @@ static int register_root_hub(struct usb_hcd *hcd)
> >   		}
> >   	}
> >   
> > +	if (le16_to_cpu(usb_dev->descriptor.bcdUSB) >= 0x0201) {
> > +		retval = usb_get_bos_descriptor(usb_dev);
> > +		if (!retval)
> > +			usb_dev->lpm_capable = usb_device_supports_lpm(usb_dev);
> > +	}
> > +
> This should be integrated with the code immediately above it, which
> also calls usb_get_bos_descriptor().  In fact, maybe you should simply
> change the existing code to check bcdUSB >= 0x0201 instead of speed ==
> USB_SPEED_SUPER.

I agree with you and will change it in v2 patch.

> >   	retval = usb_new_device (usb_dev);
> >   	if (retval) {
> >   		dev_err (parent_dev, "can't register root hub for %s, %d\n",
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index 3b71516..884d702 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -122,7 +122,7 @@ struct usb_hub *usb_hub_to_struct_hub(struct usb_device *hdev)
> >   	return usb_get_intfdata(hdev->actconfig->interface[0]);
> >   }
> >   
> > -static int usb_device_supports_lpm(struct usb_device *udev)
> > +int usb_device_supports_lpm(struct usb_device *udev)
> >   {
> >   	/* USB 2.1 (and greater) devices indicate LPM support through
> >   	 * their USB 2.0 Extended Capabilities BOS descriptor.
> > diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
> > index 7eb1e26..d5668c4 100644
> > --- a/drivers/usb/core/usb.h
> > +++ b/drivers/usb/core/usb.h
> > @@ -82,6 +82,7 @@ extern int usb_runtime_suspend(struct device *dev);
> >   extern int usb_runtime_resume(struct device *dev);
> >   extern int usb_runtime_idle(struct device *dev);
> >   extern int usb_set_usb2_hardware_lpm(struct usb_device *udev, int enable);
> > +extern int usb_device_supports_lpm(struct usb_device *udev);
> >   
> >   #else
> This will break if you build it with CONFIG_PM disabled.

Yes. Will fix it in v2 patch.

> Alan Stern

Thank you,
Baolu

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