On Wed, Mar 10, 2021 at 11:21:55AM +0200, Mika Westerberg wrote:
> Hi,
>
> On Wed, Mar 10, 2021 at 09:53:31AM +0100, Greg Kroah-Hartman wrote:
> > On Wed, Mar 10, 2021 at 09:54:44AM +0200, Mika Westerberg wrote:
> > > > > +static void tb_add_tunnel(struct tb *tb, struct tb_tunnel *tunnel)
> > > > > +{
> > > > > + struct tb_switch *sw = tunnel->dst_port->sw;
> > > > > + struct tb_cm *tcm = tb_priv(tb);
> > > > > +
> > > > > + if (tb_tunnel_is_usb3(tunnel)) {
> > > > > + sw->usb3++;
> > > > > + } else if (tb_tunnel_is_dp(tunnel)) {
> > > > > + sw->dp++;
> > > > > + /* Inform userspace about DP tunneling change */
> > > > > + kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE);
> > > >
> > > > What really "changed" here about this device that userspace now needs to
> > > > know about it?
> > >
> > > DisplayPort tunnel came up, so the "dp" attribute value changed.
> > >
> > > I'm not entirely sure we need to notify the userspace from changes like
> > > these, though. We do this when PCIe tunnel comes up already so this kind
> > > of follows that (and USB 3.x tunnel is always created at the same time
> > > the device itself is announced so does not require any change event).
> > >
> > > > > + }
> > > > > +
> > > > > + list_add_tail(&tunnel->list, &tcm->tunnel_list);
> > > > > +}
> > > > > +
> > > > > +static void tb_remove_tunnel(struct tb_tunnel *tunnel)
> > > > > +{
> > > > > + struct tb_switch *sw = tunnel->dst_port->sw;
> > > > > +
> > > > > + if (tb_tunnel_is_usb3(tunnel) && sw->usb3) {
> > > > > + sw->usb3--;
> > > > > + } else if (tb_tunnel_is_dp(tunnel) && sw->dp) {
> > > > > + sw->dp--;
> > > > > + kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE);
> > > >
> > > > Same here, what causes tunnels to be added or removed?
> > >
> > > Here the opposite, a DisplayPort tunnel was torn down so the "dp"
> > > attribute changed.
> >
> > Did just the value in the attribute change, or did the visability of
> > attributes change?
>
> The value changes.
>
> > And if it is just the value, who is going to care about this value? Is
> > userspace going to want to know this type of change? What causes this
> > to change in the first place (physical event? Virtual event? Something
> > else?)
>
> It is physical event. Typically this happens when user plugs a monitor
> to a Thunderbolt dock, or plugs it out. This value changes accordingly.
So are there other events that show up to userspace when this happens?
Like devices added/removed? If so, then sending a kobject change event
here doesn't make much sense as userspace can go re-read this based on
the fact that other things changed.
> The caring part is the userspace application, I think bolt in case of
> non-ChromeOS distro and the ChromeOS equivalent but I'm not sure if this
> is something they find useful or not. That's why I have Cc'd (hopefully
> all) the people who work with the userspace side :)
What userspace apps read this file today in any Linux distro?
thanks,
greg k-h
