RE: [PATCH v5 4/6] usb: roles: add API to get usb_role_switch by node

[Biju Das]

Hi Heikki,

> -----Original Message-----
> From: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> Sent: Monday, May 20, 2019 9:04 AM
> To: Chunfeng Yun <chunfeng.yun@xxxxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; Mark Rutland <mark.rutland@xxxxxxx>;
> Matthias Brugger <matthias.bgg@xxxxxxxxx>; Adam Thomson
> <Adam.Thomson.Opensource@xxxxxxxxxxx>; Li Jun <jun.li@xxxxxxx>;
> Badhri Jagan Sridharan <badhri@xxxxxxxxxx>; Hans de Goede
> <hdegoede@xxxxxxxxxx>; Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx>; Min Guo <min.guo@xxxxxxxxxxxx>;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> usb@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> mediatek@xxxxxxxxxxxxxxxxxxx; Biju Das <biju.das@xxxxxxxxxxxxxx>; Linus
> Walleij <linus.walleij@xxxxxxxxxx>
> Subject: Re: [PATCH v5 4/6] usb: roles: add API to get usb_role_switch by
> node
> 
> On Mon, May 20, 2019 at 10:39:11AM +0800, Chunfeng Yun wrote:
> > Hi,
> > On Fri, 2019-05-17 at 16:05 +0300, Heikki Krogerus wrote:
> > > Hi,
> > >
> > > On Fri, May 17, 2019 at 01:37:36PM +0300, Heikki Krogerus wrote:
> > > > On Tue, May 14, 2019 at 04:47:21PM +0800, Chunfeng Yun wrote:
> > > > > Add fwnode_usb_role_switch_get() to make easier to get
> > > > > usb_role_switch by fwnode which register it.
> > > > > It's useful when there is not device_connection registered
> > > > > between two drivers and only knows the fwnode which register
> > > > > usb_role_switch.
> > > > >
> > > > > Signed-off-by: Chunfeng Yun <chunfeng.yun@xxxxxxxxxxxx>
> > > > > Tested-by: Biju Das <biju.das@xxxxxxxxxxxxxx>
> > > >
> > > > Acked-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> > >
> > > Hold on. I just noticed Rob's comment on patch 2/6, where he points
> > > out that you don't need to use device graph since the controller is
> > > the parent of the connector. Doesn't that mean you don't really need
> > > this API?
> > No, I still need it.
> > The change is about the way how to get fwnode; when use device graph,
> > get fwnode by of_graph_get_remote_node(); but now will get fwnode by
> > of_get_parent();
> 
> OK, I get that, but I'm still not convinced about if something like this function
> is needed at all. I also have concerns regarding how you are using the
> function. I'll explain in comment to the patch 5/6 in this series...

FYI, Currently  I am also using this api in my patch series.
https://patchwork.kernel.org/patch/10944637/

regards,
Biju

> > > > > ---
> > > > > v5 changes:
> > > > >  1. remove linux/of.h suggested by Biju  2. add tested by Biju
> > > > >
> > > > > Note: still depends on [1]
> > > > >  [1]: [v6,08/13] usb: roles: Introduce stubs for the exiting functions in
> role.h
> > > > >       https://patchwork.kernel.org/patch/10909971/
> > > > >
> > > > > v4 changes:
> > > > >   1. use switch_fwnode_match() to find fwnode suggested by Heikki
> > > > >   2. this patch now depends on [1]
> > > > >
> > > > >  [1] [v6,08/13] usb: roles: Introduce stubs for the exiting functions in
> role.h
> > > > >     https://patchwork.kernel.org/patch/10909971/
> > > > >
> > > > > v3 changes:
> > > > >   1. use fwnodes instead of node suggested by Andy
> > > > >   2. rebuild the API suggested by Heikki
> > > > >
> > > > > v2 no changes
> > > > > ---
> > > > >  drivers/usb/roles/class.c | 24 ++++++++++++++++++++++++
> > > > > include/linux/usb/role.h  |  8 ++++++++
> > > > >  2 files changed, 32 insertions(+)
> > > > >
> > > > > diff --git a/drivers/usb/roles/class.c
> > > > > b/drivers/usb/roles/class.c index f45d8df5cfb8..4a1f09a41ec0
> > > > > 100644
> > > > > --- a/drivers/usb/roles/class.c
> > > > > +++ b/drivers/usb/roles/class.c
> > > > > @@ -135,6 +135,30 @@ struct usb_role_switch
> > > > > *usb_role_switch_get(struct device *dev)  }
> > > > > EXPORT_SYMBOL_GPL(usb_role_switch_get);
> > > > >
> > > > > +/**
> > > > > + * fwnode_usb_role_switch_get - Find USB role switch by it's
> > > > > +parent fwnode
> > > > > + * @fwnode: The fwnode that register USB role switch
> > > > > + *
> > > > > + * Finds and returns role switch registered by @fwnode. The
> > > > > +reference count
> > > > > + * for the found switch is incremented.
> > > > > + */
> > > > > +struct usb_role_switch *
> > > > > +fwnode_usb_role_switch_get(struct fwnode_handle *fwnode) {
> > > > > +	struct usb_role_switch *sw;
> > > > > +	struct device *dev;
> > > > > +
> > > > > +	dev = class_find_device(role_class, NULL, fwnode,
> switch_fwnode_match);
> > > > > +	if (!dev)
> > > > > +		return ERR_PTR(-EPROBE_DEFER);
> > > > > +
> > > > > +	sw = to_role_switch(dev);
> > > > > +	WARN_ON(!try_module_get(sw->dev.parent->driver-
> >owner));
> > > > > +
> > > > > +	return sw;
> > > > > +}
> > > > > +EXPORT_SYMBOL_GPL(fwnode_usb_role_switch_get);
> > >
> > > This function only basically converts the fwnode to usb_role_switch,
> > > but I would actually prefer that we walked through the device graph
> > > here instead of expecting the caller to do that.
> > >
> > > So this function should probable be called
> > > fwnode_to_usb_role_switch() and not fwnode_usb_role_switch_get(),
> > > but I guess you don't need it at all, right?
> > >
> > >
> > > thanks,
> > >
> >
> 
> --
> heikki