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

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?

+	}

-- 
With Best Regards,
Andy Shevchenko