linux-kernel - Re: [PATCH 1/2] usb: hub: Mark root hubs on removable devices, as removable.

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Date:   Mon, 4 Oct 2021 14:51:36 -0700
From:   Rajat Jain <rajatja@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Andrew Lunn <andrew@...n.ch>,
        Chris Chiu <chris.chiu@...onical.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        levinale@...gle.com, bleung@...gle.com, rajatxjain@...il.com,
        jsbarnes@...gle.com, pmalani@...gle.com
Subject: Re: [PATCH 1/2] usb: hub: Mark root hubs on removable devices, as removable.

Hello,

On Wed, Sep 29, 2021 at 10:30 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Wed, Sep 29, 2021 at 03:48:22PM -0700, Rajat Jain wrote:
> > Currently all usb root hubs are always marked as DEVICE_REMOVABLE_UNKNOWN
> > unconditionally. Let us try to help the users to identify the removable
> > root hubs, by checking the device on which the root hub sits. If the base
> > (parent) device on which the root hub sits, is removable (e.g. on
> > thunderbolt docks), then the roothub is also marked as removable.
> >
> > Signed-off-by: Rajat Jain <rajatja@...gle.com>
> > ---
> >  drivers/usb/core/hub.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index 86658a81d284..45d1c81b121d 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -2440,8 +2440,16 @@ static void set_usb_port_removable(struct usb_device *udev)
> >
> >       dev_set_removable(&udev->dev, DEVICE_REMOVABLE_UNKNOWN);
> >
> > -     if (!hdev)
> > +     if (!hdev) {
> > +             /*
> > +              * If the root hub sits on a removable device, mark the root hub
> > +              * removable as well. This helps with the USB root hubs sitting
> > +              * on the thunderbolt docks.
> > +              */
> > +             if (udev->dev.parent && dev_is_removable(udev->dev.parent))
> > +                     dev_set_removable(&udev->dev, DEVICE_REMOVABLE);
> >               return;
> > +     }
>
> How far "up the chain" are you going to go here?  What if the
> thunderbolt device is on a PCI device that can be removed?  What if that
> PCI device is on a PCI bus that can be removed?

PCI already takes care of that.

>
> Is a USB controller on a docking device really "removable"?
>
> The goal here is to say if this device itself is removable in the sense
> of "I can yank this out", and a roothub is not that type of device.
>
> What problem are you trying to solve with this series?

Essentially we're trying to collect some statistics (and perhaps
implement some policies) that require differentiating between internal
USB devices and external USB devices. Today, a root hub (whether
internal or external) is always shown up as "unknown". Since the
roothubs on a thunderbolt dock are removable from the system, IMHO it
is appropriate to indicate the same in sysfs.

Thanks,

Rajat

>
> thanks,
>
> greg k-h