Re: [PATCH v5 14/16] usb: documentation for usb port power off mechanisms

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On Fri, 2014-02-21 at 16:10 -0800, Dan Williams wrote:
> From: Lan Tianyu <tianyu.lan@xxxxxxxxx>
> 
> describe the mechanisms for controlling port power policy and
> discovering the port power state.
> 
> Cc: Oliver Neukum <oneukum@xxxxxxx>
> Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
> [sarah]: wordsmithing
> [djbw]: updates for peer port changes
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  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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