On Sat, 13 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>
> ---
> --- 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
>
> @@ -106,6 +107,11 @@ static inline int usb_set_usb2_hardware_lpm(struct usb_device *udev, int enable)
> return 0;
> }
>
> +static inline int usb_device_supports_lpm(struct usb_device *udev)
> +{
> + return 0;
> +}
> +
> #endif
>
> extern struct bus_type usb_bus_type;
In fact, usb_device_supports_lpm() is compiled even when CONFIG_PM
isn't set. Maybe this should be changed. But if you don't want to
change it now, you need to put the declaration outside the "#ifdef
CONFIG_PM" region. As it is, your patch is still broken (did you try
building it with CONFIG_PM unset?).
Alan Stern
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