Re: [RFC PATCH v1] usb: core: add sysfs entry for usb device state

[Alan Stern]

On Thu, May 25, 2023 at 01:31:17PM -0700, Roy Luo wrote:
> On Thu, May 25, 2023 at 12:10 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, May 25, 2023 at 11:46:23AM -0700, Roy Luo wrote:
> > > 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.
> >
> > Is there any real reason not to set port_dev->child as soon as the
> > usb_device structure is created?  If enumeration fails, the pointer can
> > be cleared.
> >
> > Alan Stern
> 
> Currently the usb core assumes the usb_device that port_dev->child points
> to is enumerated and port_dev->child->dev is registered when
> port_dev->child is present. Setting port_dev->child early would break this
> fundamental assumption, hence I'm a bit reluctant to go this way.

Well, you could remove that assumption by adding a "child_is_registered" 
flag and explicitly checking it.

Alan Stern