Re: [PATCH v5 10/16] usb: hub: Power on connected M.2 E-key connectors with power sequencing API

[Chen-Yu Tsai]

On Wed, Jul 15, 2026 at 9:25 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, Jul 15, 2026 at 04:53:40PM +0800, Chen-Yu Tsai wrote:
> > The new M.2 E-key connector can have a USB connection. For the USB device
> > on this connector to work, its power must be enabled and the W_DISABLE2#
> > signal deasserted. The connector driver handles this and provides a
> > toggle over the power sequencing API.
> >
> > This feature currently only supports a directly connected (no mux in
> > between) M.2 E-key connector. Existing USB connector types are not
> > covered. The USB A connector was recently added to the onboard devices
> > driver. USB B connectors have historically been managed by the USB
> > gadget or dual-role device controller drivers. USB C connectors are
> > handled by TCPM drivers.
> >
> > The power sequencing API does not know whether a power sequence provider
> > is not needed or not available yet, so we only request it for connectors
> > that we know need it, which at this time is just the E-key connector.
> >
> > On the USB side, the port firmware node (if present) is tied to the
> > usb_port device. This device is used to acquire the power sequencing
> > descriptor. This allows the provider to tell the different ports on one
> > hub apart.
> >
> > This feature is not implemented in the onboard USB devices driver. The
> > power sequencing API expects the consumer device to make the request,
> > but there is no device node to instantiate a platform device to tie
> > the driver to. The connector is not a child node of the USB host or
> > hub, and the graph connection is from a USB port to the connector.
> > And the connector itself already has a driver.
> >
> > Power sequencing is not directly enabled in the connector driver as
> > that would completely decouple the timing of it from the USB subsystem.
> > It would not be possible for the USB subsystem to toggle the power
> > for a power cycle or to disable the port.
>
> ...
>
> > static void usb_port_device_release(struct device *dev)
>
> >       fwnode_handle_put(dev_fwnode(dev));
> > +     /* usb_hub_create_port_device() could leave an error value */
> > +     if (!IS_ERR(port_dev->pwrseq))
> > +             pwrseq_put(port_dev->pwrseq);
>
> Hmm... I would rather make pwrseq_put() NULL and error pointer-aware, so
> it will be no-op in such cases. But I think Bart has his own opinion about
> this.
>
> >       kfree(port_dev->req);
> >       kfree(port_dev);
> >  }
>
> >               put_device(&port_dev->dev);
> > +             hub->ports[port1 - 1] = NULL;
> >               return retval;
> >       }
>
> ...
>
> > int usb_hub_create_port_device(struct usb_hub *hub, int port1)
>
> > +     port_dev->pwrseq = usb_hub_port_pwrseq_get(port_dev);
> > +     if (IS_ERR(port_dev->pwrseq)) {
> > +             retval = dev_err_probe(&port_dev->dev, PTR_ERR(port_dev->pwrseq),
> > +                                    "failed to get power sequencing descriptor\n");
> > +             goto err_put_kn;
>
> OTOH, how pwrseq can be non-NULL and at the same time port be created?

I assume by non-NULL you mean returning an error?

device_register(&port_dev->dev) is called some lines above this.

usb_port is weird in that usb_hub_create_port_device() does a bunch
of stuff that is normally done in a driver's probe function. However
usb_port's driver is just a stub driver add for userspace compatibility
reasons. See commit d99f6b4130877 ("usb: rename usb_port device objects").

So at this point the usb_port device has been added to the driver model.
Or we can just zero out port_dev->pwrseq instead? I guess that is cleaner
than having some weird check in the release function.


ChenYu