RE: [PATCH 2/2] USB: misc: Add onboard_usb_hub driver

Peter Chen
2020-09-15T07:08:33Z

> > > + hub->cfg.power_off_in_suspend =
> of_property_read_bool(dev->of_node, "power-off-in-suspend");
> > > + hub->cfg.wakeup_source = of_property_read_bool(dev->of_node,
> > > +"wakeup-source");
> >
> > Do you really need these two properties? If the device (and its
> > children if existed) has wakeup enabled, you keep power in suspend,
> > otherwise, you could close it, any exceptions?
>
> That would work for my use case, but I'm not sure it's a universally good
> configuration.
>
> I don't have a specific USB device in mind, but you could have a device that
> shouldn't lose it's context during suspend or keep operating autonomously (e.g.
> a sensor with a large buffer collecting samples). Not sure if something like this
> exists in the real though.
>
> I'm not an expert, but it seems there are USB controllers with wakeup support
> which is always enabled. A board with such a controller then couldn't have a
> policy to power down the hub regardless of wakeup capable devices being
> connected.
>

Whether or not it is a wakeup_source, it could get through its or its children's /sys/../power/wakeup
value, you have already used usb_wakeup_enabled_descendants to know it. If the onboard HUB
needs to reflect wakeup signal, it should not power off its regulator.

For another property power-off-in-suspend, I think it is also a user option, but not a hardware feature.

If (wakeup-source || ! power-off-in-suspend)
power off;
else
keep power;

Peter