RE: port power is on again after turning off by user space

[Peter Chen <peter.chen@nxp.com>]

 
> > > Hi Alan,
> > >
> > > I use one HUB power control application
> > >
> (https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.
> com%2Fmvp%2Fuhubctl&data=04%7C01%7Cpeter.chen%40nxp.com%7C
> 736ece19bc7a430c98b808d8a0b6975c%7C686ea1d3bc2b4c6fa92cd99c5c3016
> 35%7C0%7C0%7C637436053362151022%7CUnknown%7CTWFpbGZsb3d8eyJ
> WIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7
> C1000&sdata=lptf1XO5yeb6lQbAFlKUrZ%2BEX5ATXQRftGwm26WowFA%
> 3D&reserved=0) 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.
> >
> > Seems in this case the port need claimed by user app, I am seeing this
> > commit
> >
> > commit fbaecff06a7db4defa899a664fe2758e5161b39d
> > Author: Deepak Das <deepakdas.linux@gmail.com>
> > Date:   Wed Jan 21 23:39:58 2015 +0530
> >
> >     usb: core: hub: modify hub reset logic in hub driver
> >
> >     Currently if port power is turned off by user on hub port
> >     using USBDEVFS then port power is turned back ON
> >     by hub driver.
> >     This commit modifies hub reset logic in hub_port_connect() to prevent
> >     hub driver from turning back the port power ON if port is not owned
> >     by kernel.
> >
> >     Signed-off-by: Deepak Das <deepakdas.linux@gmail.com>
> >     Acked-by: Alan Stern <stern@rowland.harvard.edu>
> >     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index
> > b4bfa3a..3e9c4d4 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -4655,9 +4655,13 @@ static void hub_port_connect(struct usb_hub
> > *hub, int port1, u16 portstatus,
> >         if (!(portstatus & USB_PORT_STAT_CONNECTION) ||
> >                         test_bit(port1, hub->removed_bits)) {
> >
> > -               /* maybe switch power back on (e.g. root hub was reset)
> */
> > +               /*
> > +                * maybe switch power back on (e.g. root hub was reset)
> > +                * but only if the port isn't owned by someone else.
> > +                */
> >                 if (hub_is_port_power_switchable(hub)
> > -                               && !port_is_power_on(hub,
> portstatus))
> > +                               && !port_is_power_on(hub,
> portstatus)
> > +                               && !port_dev->port_owner)
> >                         set_port_feature(hdev, port1,
> > USB_PORT_FEAT_POWER);
> >
> >                 if (portstatus & USB_PORT_STAT_ENABLE)
> >
> 
> Yes, I saw this commit. But the port is owned by kernel, the device on the port
> could be enumerated by kernel, just the power on the port could be changed by
> user space.
> 

I find this issue has discussed there, but I can't open the URL: https://bit.ly/2JzczjZ
Below the description from: https://github.com/mvp/uhubctl.
Their workarounds are not good.

Power comes back on after few seconds on Linux

Some device drivers in kernel are surprised by USB device
being turned off and automatically try to power it back on.

You can use option -r N where N is some number from 10 to 1000
to fix this - uhubctl will try to turn power off many times in quick
succession, and it should suppress that. This may be eventually fixed
in kernel, see more discussion here.

Disabling USB authorization for device in question before
turning power off with uhubctl should help:

echo 0 > sudo tee /sys/bus/usb/devices/${location}.${port}/authorized
If your device is USB mass storage, invoking udisksctl before calling uhubctl
should help too:

sudo udisksctl power-off --block-device /dev/disk/...`
sudo uhubctl -a off ...
 
Peter