linux-kernel - Re: [PATCH v2 6/9] usb: roles: Find the muxes by also matching against the device node

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Date:   Tue, 12 Feb 2019 10:50:33 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Jun Li <jun.li@....com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Chen Yu <chenyu56@...wei.com>,
        Hans de Goede <hdegoede@...hat.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/9] usb: roles: Find the muxes by also matching
 against the device node

Hi,

On Tue, Feb 12, 2019 at 06:03:42AM +0000, Jun Li wrote:
> > > return dev_fwnode(dev->parent) == fwnode;
> > 
> > That's actually not the case. struct usb_role_switch_desc has a member for fwnode,
> > and that's what we use with the actual mux device. Check
> > usb_role_switch_register():
> > 
> >         ...
> >         sw->dev.fwnode = desc->fwnode;
> >         ...
> > 
> > Sorry for not realizing it before.
> 
> So desc->fwnode should be initialized before do usb_role_switch_register()?
> But seems usb_role_switch_desc is a read-only object so can't be set at runtime.

It can. Even though usb_role_switch_register() takes read-only
parameter, nothing's preventing you from passing data even from the
stack (the content of the descriptor is copied in any case).

Expecting the descriptor to be read-only just means it can be
read-only, but it does not have to be.

> usb_controller_node {
> 	...
> 	usb-role-switch;
> 
> 	port {
> 		sw_provider_node: endpoint {
> 			remote-endpoint = <&sw_consumer_node>;
> 		};
> 	};
> };
> 
> typec_node {
> 	...
> 	port {
> 		sw_consumer_node: endpoint {
> 			remote-endpoint = <&sw_provider_node>;
> 		};
> 	};
> };

That looks roughly correct to me.


thanks,

-- 
heikki