On Thu, May 25, 2023 at 11:02 AM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, May 25, 2023 at 05:38:18PM +0000, Roy Luo wrote: > > Expose usb device state to userland as the information is useful in > > detecting non-compliant setups and diagnosing enumeration failures. > > For example: > > - End-to-end signal integrity issues: the device would fail port reset > > repeatedly and thus be stuck in POWERED state. > > - Charge-only cables (missing D+/D- lines): the device would never enter > > POWERED state as the HC would not see any pullup. > > > > What's the status quo? > > We do have error logs such as "Cannot enable. Maybe the USB cable is bad?" > > to flag potential setup issues, but there's no good way to expose them to > > userspace. > > > > Why add a sysfs entry in struct usb_port instead of struct usb_device? > > The struct usb_device is not device_add() to the system until it's in > > ADDRESS state hence we would miss the first two states. The struct > > usb_port is a better place to keep the information because its life > > cycle is longer than the struct usb_device that is attached to the port. > > > > Signed-off-by: Roy Luo <royluo@xxxxxxxxxx> > > --- > > > diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h > > index e23833562e4f..110143568c77 100644 > > --- a/drivers/usb/core/hub.h > > +++ b/drivers/usb/core/hub.h > > @@ -84,8 +84,10 @@ struct usb_hub { > > * @peer: related usb2 and usb3 ports (share the same connector) > > * @req: default pm qos request for hubs without port power control > > * @connect_type: port's connect type > > + * @state: device state of the usb device attached to the port > > This member is essentially a duplicate of the .child member of the > usb_port structure. That is, it points to the .state member of the > child device instead of to the child device itself, but this is pretty > much the same thing. You could replace *(port_dev->state) with > port_dev->child->state. > Alan, thanks for the quick response! Yes, port_dev->state is indeed the same as port_dev->child->state. However, I still add port_dev->state because port_dev->child won't be assigned until the corresponding usb_device is in ADDRESS state. I wish I can assign get port_dev->child assigned earlier, but I think the current design - assign port_dev->child and device_add() after ADDRESS state - also makes sense because there are many ways that the enumeration could fail in the early stage. By adding port_dev->state, I can link usb_device->state to usb_port as soon as the usb_device is created to get around the limitation of port_dev->child. I would be very happy to hear other ideas. > > diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c > > index 06a8f1f84f6f..7f3430170115 100644 > > --- a/drivers/usb/core/port.c > > +++ b/drivers/usb/core/port.c > > @@ -160,6 +160,19 @@ static ssize_t connect_type_show(struct device *dev, > > } > > static DEVICE_ATTR_RO(connect_type); > > > > +static ssize_t state_show(struct device *dev, > > + struct device_attribute *attr, char *buf) > > +{ > > + struct usb_port *port_dev = to_usb_port(dev); > > + enum usb_device_state state = USB_STATE_NOTATTACHED; > > + > > + if (port_dev->state) > > + state = *port_dev->state; > > + > > + return sprintf(buf, "%s\n", usb_state_string(state)); > > This races with device addition and removal (and with device state > changes). To prevent these races, you have to hold the > device_state_lock spinlock while accessing the child device and its > state. > > Unfortunately that spinlock is private to hub.c, so you will have to > make it public before you can use it here. > > Alan Stern