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Date: Wed, 19 Feb 2020 01:58:38 +0000 From: Peter Chen <peter.chen@....com> To: Heikki Krogerus <heikki.krogerus@...ux.intel.com> CC: Felipe Balbi <balbi@...nel.org>, Chunfeng Yun <chunfeng.yun@...iatek.com>, Bin Liu <b-liu@...com>, Benson Leung <bleung@...omium.org>, Prashant Malani <pmalani@...omium.org>, Mika Westerberg <mika.westerberg@...ux.intel.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org> Subject: Re: [PATCH 5/9] usb: roles: Provide the switch drivers handle to the switch in the API 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
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