On Mon, Feb 24, 2014 at 2:17 AM, Oliver Neukum <oneukum@xxxxxxx> wrote:
> 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"
Ok.
>> +* 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.
I'm not sure I grok this comment? Specifically I am referring to this logic:
usb_port_suspend() {
[..]
if (status == 0 && !udev->do_remote_wakeup && udev->persist_enabled) {
pm_runtime_put_sync(&port_dev->dev);
port_dev->did_runtime_put = true;
}
[..]
}
I have a follow-on patch to go clear ->do_remote_wakeup on a hub once
all its downstream ports are suspended, but until then the simply does
not allow such ports to suspend.
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