On Fri, 2014-02-21 at 16:10 -0800, Dan Williams wrote:
> From: Lan Tianyu <[email protected]>
>
> describe the mechanisms for controlling port power policy and
> discovering the port power state.
>
> Cc: Oliver Neukum <[email protected]>
> Signed-off-by: Lan Tianyu <[email protected]>
> [sarah]: wordsmithing
> [djbw]: updates for peer port changes
> Signed-off-by: Dan Williams <[email protected]>
> ---
> Documentation/usb/power-management.txt | 237
> ++++++++++++++++++++++++++++++++
> 1 files changed, 237 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/usb/power-management.txt
> b/Documentation/usb/power-management.txt
> index 1392b61d6ebe..e67c1d4d1994 100644
> --- a/Documentation/usb/power-management.txt
> +++ b/Documentation/usb/power-management.txt
> @@ -5,6 +5,25 @@
> October 28, 2010
>
>
> + Contents:
> + ---------
> + * What is Power Management?
> + * What is Remote Wakeup?
> + * When is a USB device idle?
> + * Forms of dynamic PM
> + * The user interface for dynamic PM
> + * Changing the default idle-delay time
> + * Warnings
> + * The driver interface for Power Management
> + * The driver interface for autosuspend and autoresume
> + * Other parts of the driver interface
> + * Mutual exclusion
> + * Interaction between dynamic PM and system PM
> + * xHCI hardware link PM
> + * USB Port Power Control
> + * User Interface for Port Power Control
> + * Suggested Userspace Port Power Policy
> +
>
> What is Power Management?
> -------------------------
> @@ -516,3 +535,221 @@ relevant attribute files is usb2_hardware_lpm.
> driver will enable hardware LPM for the device. You
> can write y/Y/1 or n/N/0 to the file to enable/disable
> USB2 hardware LPM manually. This is for test purpose mainly.
> +
> +
> + USB Port Power Control
> + ----------------------
> +
> +In addition to suspending endpoint devices and enabling hardware
> +controlled link power management, the USB subsystem also has the
> +capability to disable power to individual ports. Power is controlled
Not necessary individual ports. You explain the limitations of ganged
switching further below. I'd prefer "ports under some conditions"
> +* wakeup note: the implementation does not allow a port connected to a
> + device with wakeup capability to be powered off.
The capability may be there. It just mustn't be enabled.
Regards
Oliver
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