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From:   Peter Chen <peter.chen@nxp.com>
To:     Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC:     Felipe Balbi <balbi@kernel.org>,
        Chunfeng Yun <chunfeng.yun@mediatek.com>,
        Bin Liu <b-liu@ti.com>, Benson Leung <bleung@chromium.org>,
        Prashant Malani <pmalani@chromium.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: Re: [PATCH 5/9] usb: roles: Provide the switch drivers handle to the
 switch in the API
Thread-Topic: [PATCH 5/9] usb: roles: Provide the switch drivers handle to the
 switch in the API
Thread-Index: AQHV4nD6G15oErWo00iXG8zLCuhxYqgZHzyAgAd0koCAAFRlgIAA4yEA
Date:   Wed, 19 Feb 2020 01:58:38 +0000
Message-ID: <20200219015840.GC8602@b29397-desktop>
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On 20-02-18 14:25:45, Heikki Krogerus wrote:
> Hi,
>=20
> On Tue, Feb 18, 2020 at 07:23:41AM +0000, Peter Chen wrote:
> > > > @@ -1118,6 +1119,7 @@ static int ci_hdrc_probe(struct platform_devi=
ce *pdev)
> > > >  	}
> > > > =20
> > > >  	if (ci_role_switch.fwnode) {
> > > > +		ci_role_switch.driver_data =3D ci;
> > > >  		ci->role_switch =3D usb_role_switch_register(dev,
> > > >  					&ci_role_switch);
> >=20
> > Why the struct usb_role_switch_desc needs drvdata, the struct
> > usb_role_switch has already one?
>=20
> I'm assuming that you are asking why not just register the switch,
> and then call usb_role_switch_set_drvdata(), right?

Yes.

>=20
> 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.
>=20
> 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.
>=20

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

--=20

Thanks,
Peter Chen=