Re: [PATCH 5/9] usb: roles: Provide the switch drivers handle to the switch in the API

Peter Chen
2020-02-19T01:58:45Z

On 20-02-18 14:25:45, Heikki Krogerus wrote:
> Hi,
>
> On Tue, Feb 18, 2020 at 07:23:41AM +0000, Peter Chen wrote:
> > > > @@ -1118,6 +1119,7 @@ static int ci_hdrc_probe(struct platform_device *pdev)
> > > > }
> > > >
> > > > if (ci_role_switch.fwnode) {
> > > > + ci_role_switch.driver_data = ci;
> > > > ci->role_switch = usb_role_switch_register(dev,
> > > > &ci_role_switch);
> >
> > Why the struct usb_role_switch_desc needs drvdata, the struct
> > usb_role_switch has already one?
>
> I'm assuming that you are asking why not just register the switch,
> and then call usb_role_switch_set_drvdata(), right?

Yes.

>
> That may create a race condition where the switch is accessed before
> the driver data is available. That can happen for example if the
> switch is exposed to the user space.
>
> To play it safe, supplying the driver data as part of the descriptor.
> That way we can be sure that the driver data is always available
> the moment the switch is registered.
>

Then, you may use the uniform way for the driver. Some may have
race condition like you said.

--

Thanks,
Peter Chen