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.
> 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.
Alan Stern
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