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From: Peter Chen <peter.chen@nxp.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: port power is on again after turning off by user space
Date: Tue, 15 Dec 2020 03:31:04 +0000	[thread overview]
Message-ID: <DBBPR04MB79793525394F70DE397E24038BC60@DBBPR04MB7979.eurprd04.prod.outlook.com> (raw)

Hi Alan,

I use one HUB power control application (https://github.com/mvp/uhubctl) to investigate power switchable HUB, and
find the kernel turns port power on again at drivers/usb/core/hub.c, after port power is turned off by user space.

5122                 if (hub_is_port_power_switchable(hub)
5123                                 && !port_is_power_on(hub, portstatus)
5124                                 && !port_dev->port_owner)
5125                         set_port_feature(hdev, port1, USB_PORT_FEAT_POWER);

The main sequence for testing turn port power off like below:

- uhubctl sends command to turn specifc port (eg, 2-1.4) power off.
- devio at kernel gets that command, and send to hub.
- port power is off, the hub_event is triggered due to port status is changed.
- usb_disconnect is called, but port power is on again by kernel at function hub_port_connect.

I can't find the code history why the port power needs to turn on after device is disconnected, do you know why?
Any sugguestions to fix it? Thanks.

Best regards,
Peter Chen
 


             reply	other threads:[~2020-12-15  3:32 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-15  3:31 Peter Chen [this message]
2020-12-15  5:02 ` port power is on again after turning off by user space Jun Li
2020-12-15  5:14   ` Peter Chen
2020-12-15  9:57     ` Peter Chen
2020-12-15 15:55       ` Alan Stern
2020-12-16  2:56         ` Peter Chen
2020-12-16 15:51           ` Alan Stern
2020-12-21  5:37             ` Peter Chen
2020-12-21 16:25               ` Alan Stern
2020-12-22  2:02                 ` Peter Chen
2020-12-22  2:35                   ` Alan Stern

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