linux-kernel - RE: [PATCH v9 2/4] gadget: Support for the usb charger framework

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Message-ID: <AM4PR04MB2130E03385128C1CD22553E7899F0@AM4PR04MB2130.eurprd04.prod.outlook.com>
Date:	Wed, 6 Apr 2016 13:49:04 +0000
From:	Jun Li <jun.li@....com>
To:	Felipe Balbi <balbi@...nel.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Peter Chen <hzpeterchen@...il.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Peter Chen <peter.chen@...escale.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lee Jones <lee.jones@...aro.org>,
	"Mark Brown" <broonie@...nel.org>,
	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	"patches@...nsource.wolfsonmicro.com" 
	<patches@...nsource.wolfsonmicro.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB <linux-usb@...r.kernel.org>,
	"device-mainlining@...ts.linuxfoundation.org" 
	<device-mainlining@...ts.linuxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v9 2/4] gadget: Support for the usb charger framework

Hi

> -----Original Message-----
> From: Felipe Balbi [mailto:balbi@...nel.org]
> Sent: Wednesday, April 06, 2016 8:56 PM
> To: Jun Li <jun.li@....com>; Baolin Wang <baolin.wang@...aro.org>; Peter
> Chen <hzpeterchen@...il.com>
> Cc: Greg KH <gregkh@...uxfoundation.org>; Sebastian Reichel
> <sre@...nel.org>; Dmitry Eremin-Solenikov <dbaryshkov@...il.com>; David
> Woodhouse <dwmw2@...radead.org>; Peter Chen <peter.chen@...escale.com>;
> Alan Stern <stern@...land.harvard.edu>; r.baldyga@...sung.com; Yoshihiro
> Shimoda <yoshihiro.shimoda.uh@...esas.com>; Lee Jones
> <lee.jones@...aro.org>; Mark Brown <broonie@...nel.org>; Charles Keepax
> <ckeepax@...nsource.wolfsonmicro.com>; patches@...nsource.wolfsonmicro.com;
> Linux PM list <linux-pm@...r.kernel.org>; USB <linux-usb@...r.kernel.org>;
> device-mainlining@...ts.linuxfoundation.org; LKML <linux-
> kernel@...r.kernel.org>
> Subject: RE: [PATCH v9 2/4] gadget: Support for the usb charger framework
> 
> 
> Hi,
> 
> Jun Li <jun.li@....com> writes:
> >> >> On 6 April 2016 at 15:19, Peter Chen <hzpeterchen@...il.com> wrote:
> >> >> > On Fri, Apr 01, 2016 at 03:21:50PM +0800, Baolin Wang wrote:
> >> >> >>
> >> >> >> @@ -563,6 +564,8 @@ struct usb_gadget_ops {
> >> >> >>       struct usb_ep *(*match_ep)(struct usb_gadget *,
> >> >> >>                       struct usb_endpoint_descriptor *,
> >> >> >>                       struct usb_ss_ep_comp_descriptor *);
> >> >> >> +     /* get the charger type */
> >> >> >> +     enum usb_charger_type (*get_charger_type)(struct
> >> >> >> + usb_gadget *);
> >> >> >>  };
> >> >> >
> >> >> > Since we already have get_charger_type callback at usb_charger
> >> >> > structure, why we still need this API at usb_gadget_ops?
> >> >>
> >> >> In case some users want to get charger type at gadget level.
> >> >>
> >> > Why gadget needs to know charger type? I also don't catch the
> >> > intent of
> >>
> >> because some gadgets need to call usb_gadget_vbus_draw(), although
> >> for that they need power in mA rather.
> >
> > In below change of usb_gadget_vbus_draw(), already can get charger
> > type via usb_charger_get_type().
> >
> > static inline int usb_gadget_vbus_draw(struct usb_gadget *gadget,
> > unsigned mA)  {
> > +       enum usb_charger_type type;
> > +
> > +       if (gadget->charger) {
> > +               type = usb_charger_get_type(gadget->charger);
> > +               usb_charger_set_cur_limit_by_type(gadget->charger, type,
> mA);
> > +       }
> > +
> >         if (!gadget->ops->vbus_draw)
> >                 return -EOPNOTSUPP;
> >         return gadget->ops->vbus_draw(gadget, mA);
> >
> > Could you detail in what situation gadget->ops-> get_charger_type() is
> used?
> 
> isn't it right there in the code ? Isn't usb_gadget_vbus_draw() calling
> it ? What did I miss here ?

Well, that's true, so my real meaning is why gadget need get charger type
via another new api gadget->ops->get_charger_type().
 
> 
> >> > This api, as my understanding, gadget only need report gadget state
> >> changes.
> >> > All information required for usb charger is charger type and gadget
> >> state.
> >>
> >> you're making an assumption about how the HW is laid out which might
> >> not be true.
> >>
> >
> > What other information you refer to here? Or what I am not aware of?
> 
> what I'm trying to say is that you're assuming gadgets don't need to know
> anything other than charger type and gadget state (suspended, resume,
> enumerated, default state, addressed, etc), but that might not be true for
> all UDCs. You can't make that assumption that charger type and gadget
> state is enough. The real question is what do we need *now*, but still
> keep in mind that what we need *now* might be valid 2 years from now, so
> API needs to be a little flexible.

Get your point, flexible, I just thought create an api without any user
for existing case/spec, wouldn't it be better to let the real user add it
later when it's needed.

> 
> cheers
> 
> --
> balbi