On Mon, May 04, 2015 at 11:15:30AM +0800, Lu Baolu wrote:
> This patch adds a new entry pointer in hc_driver. With this new entry,
> USB core can notify host driver when something happens and host driver
> is willing to be notified. One use case of this interface comes from
> xHCI compatible host controller driver.
>
> The xHCI spec is designed to allow an xHC implementation to cache the
> endpoint state. Caching endpoint state allows an xHC to reduce latency
> when handling ERDYs and other USB asynchronous events. However holding
> this state in xHC consumes resources and power. The xHCI spec designs
> some methods through which host controller driver can hint xHC about
> how to optimize its operation, e.g. to determine when it holds state
> internally or pushes it out to memory, when to power down logic, etc.
>
> When a USB device is going to suspend, states of all endpoints cached
> in the xHC should be pushed out to memory to save power and resources.
> Vice versa, when a USB device resumes, those states should be brought
> back to the cache. USB core suspends or resumes a USB device by sending
> set/clear port feature requests to the parent hub where the USB device
> is connected. Unfortunately, these operations are transparent to xHCI
> driver unless the USB device is plugged in a root port. This patch
> utilizes the notify interface to notify xHCI driver whenever a USB
> device's power state is changed.
>
> It is harmless if a USB devices under USB 3.0 host controller suspends
> or resumes without a notification to hcd driver. However there may be
> less opportunities for power savings and there may be increased latency
> for restarting an endpoint. The precise impact will be different for
> each xHC implementation. It all depends on what an implementation does
> with the hints.
>
> Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
> ---
> drivers/usb/core/generic.c | 10 ++++++++--
> drivers/usb/core/hcd.c | 23 +++++++++++++++++++++++
> include/linux/usb/hcd.h | 11 ++++++++++-
> 3 files changed, 41 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/core/generic.c b/drivers/usb/core/generic.c
> index 358ca8d..92bee33 100644
> --- a/drivers/usb/core/generic.c
> +++ b/drivers/usb/core/generic.c
> @@ -211,8 +211,12 @@ static int generic_suspend(struct usb_device *udev,
> pm_message_t msg)
> /* Non-root devices don't need to do anything for FREEZE or PRETHAW */
> else if (msg.event == PM_EVENT_FREEZE || msg.event == PM_EVENT_PRETHAW)
> rc = 0;
> - else
> + else {
> + hcd_notify(udev, HCD_MSG_DEV_SUSPEND, &msg);
> rc = usb_port_suspend(udev, msg);
> + if (rc)
> + hcd_notify(udev, HCD_MSG_DEV_RESUME, &msg);
> + }
>
> return rc;
> }
> @@ -228,8 +232,10 @@ static int generic_resume(struct usb_device *udev,
> pm_message_t msg)
> */
> if (!udev->parent)
> rc = hcd_bus_resume(udev, msg);
> - else
> + else {
> rc = usb_port_resume(udev, msg);
> + hcd_notify(udev, HCD_MSG_DEV_RESUME, &msg);
> + }
> return rc;
> }
>
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 45a915c..725d611 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -2289,6 +2289,29 @@ void usb_hcd_resume_root_hub (struct usb_hcd *hcd)
> }
> EXPORT_SYMBOL_GPL(usb_hcd_resume_root_hub);
>
> +/**
> + * hcd_notify - notify hcd driver with a message
> + * @udev: USB device
> + * @type: message type of this notification
> + * @data: message type specific data
> + *
> + * Call back to hcd driver to notify an event.
> + */
> +void hcd_notify(struct usb_device *udev,
> + enum hcd_notification_type type, void *data)
> +{
> + struct usb_hcd *hcd;
> +
> + if (!udev)
> + return;
> +
> + hcd = bus_to_hcd(udev->bus);
> +
> + if (hcd->driver->notify)
> + hcd->driver->notify(hcd, udev, type, data);
> +}
> +EXPORT_SYMBOL_GPL(hcd_notify);
Why does this have to be exported?
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