Re: [PATCH v6 10/16] usb: hub: Power on connected M.2 E-key connectors with power sequencing API

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Jul 21, 2026 at 02:54:05PM +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.
> 
> Sashiko mentions possible use-after-free of hub->ports from the sysfs
> callbacks. This is actually not possible, since the sysfs callbacks
> acquire the hub device and its lock, and then check if it is in the
> process of disconnect / removal. If it is, then the callbacks just
> error out.

...

> static inline bool hub_is_port_power_switchable(struct usb_hub *hub)

>  	if (!hub)
>  		return false;
>  	hcs = hub->descriptor->wHubCharacteristics;
> -	return (le16_to_cpu(hcs) & HUB_CHAR_LPSM) < HUB_CHAR_NO_LPSM;
> +	if ((le16_to_cpu(hcs) & HUB_CHAR_LPSM) < HUB_CHAR_NO_LPSM)
> +		return true;

> +	/* check for controllable external power sequencers */
> +	for (unsigned int i = 0; i < hub->hdev->maxchild; i++)
> +		if (hub->ports[i] && hub->ports[i]->pwrseq)
> +			return true;

Missing {}.

> +	return false;

-- 
With Best Regards,
Andy Shevchenko