On Wed, May 04, 2016 at 11:40:56AM +0300, Roger Quadros wrote: > On 04/05/16 11:03, Jun Li wrote: > > Hi > > > >> -----Original Message----- > >> From: Roger Quadros [mailto:rogerq@xxxxxx] > >> Sent: Wednesday, May 04, 2016 2:37 PM > >> To: Peter Chen <hzpeterchen@xxxxxxxxx> > >> Cc: Jun Li <jun.li@xxxxxxx>; stern@xxxxxxxxxxxxxxxxxxx; balbi@xxxxxxxxxx; > >> gregkh@xxxxxxxxxxxxxxxxxxx; peter.chen@xxxxxxxxxxxxx; > >> dan.j.williams@xxxxxxxxx; jun.li@xxxxxxxxxxxxx; > >> mathias.nyman@xxxxxxxxxxxxxxx; tony@xxxxxxxxxxx; Joao.Pinto@xxxxxxxxxxxx; > >> abrestic@xxxxxxxxxxxx; r.baldyga@xxxxxxxxxxx; linux-usb@xxxxxxxxxxxxxxx; > >> linux-kernel@xxxxxxxxxxxxxxx; linux-omap@xxxxxxxxxxxxxxx > >> Subject: Re: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core > >> > >> Peter, > >> > >> On 04/05/16 06:35, Peter Chen wrote: > >>> On Tue, May 03, 2016 at 06:44:46PM +0300, Roger Quadros wrote: > >>>> Hi, > >>>> > >>>> On 03/05/16 10:06, Jun Li wrote: > >>>>> Hi > >>>>> > >>>>>>>>>>>>> /** > >>>>>>>>>>>>> + * usb_gadget_start - start the usb gadget controller and > >>>>>>>>>>>>> +connect to bus > >>>>>>>>>>>>> + * @gadget: the gadget device to start > >>>>>>>>>>>>> + * > >>>>>>>>>>>>> + * This is external API for use by OTG core. > >>>>>>>>>>>>> + * > >>>>>>>>>>>>> + * Start the usb device controller and connect to bus > >>>>>>>>>>>>> +(enable > >>>>>> pull). > >>>>>>>>>>>>> + */ > >>>>>>>>>>>>> +static int usb_gadget_start(struct usb_gadget *gadget) { > >>>>>>>>>>>>> + int ret; > >>>>>>>>>>>>> + struct usb_udc *udc = NULL; > >>>>>>>>>>>>> + > >>>>>>>>>>>>> + dev_dbg(&gadget->dev, "%s\n", __func__); > >>>>>>>>>>>>> + mutex_lock(&udc_lock); > >>>>>>>>>>>>> + list_for_each_entry(udc, &udc_list, list) > >>>>>>>>>>>>> + if (udc->gadget == gadget) > >>>>>>>>>>>>> + goto found; > >>>>>>>>>>>>> + > >>>>>>>>>>>>> + dev_err(gadget->dev.parent, "%s: gadget not > >> registered.\n", > >>>>>>>>>>>>> + __func__); > >>>>>>>>>>>>> + mutex_unlock(&udc_lock); > >>>>>>>>>>>>> + return -EINVAL; > >>>>>>>>>>>>> + > >>>>>>>>>>>>> +found: > >>>>>>>>>>>>> + ret = usb_gadget_udc_start(udc); > >>>>>>>>>>>>> + if (ret) > >>>>>>>>>>>>> + dev_err(&udc->dev, "USB Device Controller didn't > >>>>>>>> start: %d\n", > >>>>>>>>>>>>> + ret); > >>>>>>>>>>>>> + else > >>>>>>>>>>>>> + usb_udc_connect_control(udc); > >>>>>>>>>>>> > >>>>>>>>>>>> For drd, it's fine, but for real otg, gadget connect should > >>>>>>>>>>>> be done by > >>>>>>>>>>>> loc_conn() instead of gadget start. > >>>>>>>>>>> > >>>>>>>>>>> It is upto the OTG state machine to call gadget_start() when > >>>>>>>>>>> it needs to connect to the bus (i.e. loc_conn()). I see no > >>>>>>>>>>> point in calling gadget start before. > >>>>>>>>>>> > >>>>>>>>>>> Do you see any issue in doing so? > >>>>>>>>>> > >>>>>>>>>> This is what OTG state machine does: > >>>>>>>>>> case OTG_STATE_B_PERIPHERAL: > >>>>>>>>>> otg_chrg_vbus(otg, 0); > >>>>>>>>>> otg_loc_sof(otg, 0); > >>>>>>>>>> otg_set_protocol(fsm, PROTO_GADGET); > >>>>>>>>>> otg_loc_conn(otg, 1); > >>>>>>>>>> break; > >>>>>>>> > >>>>>>>> On second thoughts, after seen the OTG state machine. > >>>>>>>> otg_set_protocol(fsm, PROTO_GADGET); is always followed by > >>>>>>>> otg_loc_conn(otg, 1); And whenever protocol changes to anything > >>>>>>>> other the PROTO_GADGET, we use otg_loc_conn(otg, 0); > >>>>>>>> > >>>>>>>> So otg_loc_conn seems redundant. Can we just get rid of it? > >>>>>>>> > >>>>>>>> usb_gadget_start() implies that gadget controller starts up and > >>>>>>>> enables pull. > >>>>>>>> usb_gadget_stop() implies that gadget controller disables pull > >>>>>>>> and > >>>>>> stops. > >>>>>>>> > >>>>>>>> > >>>>>>>> Can you please explain why just these 2 APIs are not sufficient > >>>>>>>> for full OTG? > >>>>>>>> > >>>>>>>> Do we want anything to happen between gadget controller > >>>>>>>> start/stop and pull on/off? > >>>>>>> > >>>>>>> "loc_conn" is a standard output parameter in OTG spec, it deserves > >>>>>>> a separate api, yes, current implementation of OTG state machine > >>>>>>> code seems allow you to combine the 2 things into one, but don't > >>>>>>> do that, because they do not always happen together, e.g. for > >>>>>>> peripheral only B device (also a part OTG spec: section 7.3), will > >>>>>>> be fixed in gadget mode, but it will do gadget connect and > >>>>>>> disconnect in its diff states, so, to make the framework common, > >> let's keep them separated. > >>>>>> > >>>>>> I'm sorry but I didn't understand your comment about "it will do > >>>>>> gadget connect and disconnect in its diff states" > >>>>> > >>>>> Gadget connect means loc_conn(1). > >>>>> > >>>>>> > >>>>>> I am reading the OTG v2.0 specification and loc_conn is always true > >>>>>> when b_peripheral or a_peripheral is true and false otherwise. > >>>>> > >>>>> If you only talk about these 2 states, yes, loc_conn is ture. > >>>>> > >>>>>> > >>>>>> loc_conn is just an internal state variable and it corresponds to > >>>>>> our > >>>>>> gadget_start/stop() state. > >>>>> > >>>>> It's not an internal variable, there are OTG state machine > >>>>> parameters tables(table 7-x) in OTG spec which have clear lists > >>>>> which are "internal variable", which are "input", which are "output"... > >>>>> > >>>>> Those APIs are driven directly from OTG spec, easily understood so > >>>>> code reader can know what's those APIs for. For real OTG, I don't > >>>>> see the benefit if get rid of it. > >>>> > >>>> OK, no issues if we don't get rid of it. But I am still in favor of > >>>> doing a connect in usb_gadget_start(), because > >>>> > >>>> 1) If we split connect/disconnect() and usb_gadget_start/stop() then > >>>> there is additional overhead of keeping track whether connect was > >>>> called or not during usb_gadget_stop(). Plus we need to take care > >>>> that users don't call connect/disconnect outside of start/stop. It is > >> just complicating things. > >>>> > >>>> 2) for many controllers there is no difference between run/stop and > >>>> connect/disconnect. i.e. a single register bit controls both. > >>>> > >>>> 3) it fits well with the OTG specification. OTG specification says > >>>> that loc_conn *variable* must be true *after* the device has signalled > >> a connect. > >>>> So OTG state machine can safely set loc_conn variable to true after > >>>> doing otg_set_protocol(fsm, PROTO_GADGET); and set it to false > >> otherwise. > >>>> > >>>> Note, OTG specification does not say to take any action based on > >> loc_conn. > >>>> It is just a connect indicator variable. So we might have to fix this > >>>> in the OTG state machine. > >>>> > >>>> My suggestion is to keep it simple for now. Try the OTG > >>>> implementation, and later if we find issues then extend it as required. > >>>> > >>> > >>> Just talked with Jun, he is worried if loc_conn != pullup_dp at some > >>> situations. So, how about only calling start gadget at > >>> usb_start_gadget, > >> > >> Which situations? > > > > When to pull-up DP is decided by application (while vbus is on), > > not only by driver state machine. > > So when OTG state is B_PERIPHERAL or A_PERIPHERAL we still want DP pull-up > to be disabled? > > > > >> > >>> and pullup_dp at drd_set_state (see below). > >>> > >>> > >>> static void drd_set_state(struct otg_fsm *fsm, enum usb_otg_state > >>> new_state) { > >>> struct usb_otg *otg = container_of(fsm, struct usb_otg, fsm); > >>> > >>> if (otg->state == new_state) > >>> return; > >>> > >>> fsm->state_changed = 1; > >>> dev_dbg(otg->dev, "otg: set state: %s\n", > >>> usb_otg_state_string(new_state)); > >>> switch (new_state) { > >>> case OTG_STATE_B_IDLE: > >>> + usb_udc_vbus_handler(gadget, false); > >> > >> This is redundant, When we switch from PROTO_GADGET to PROTO_UNDEF we do a > >> usb_gadget_stop(), and a usb_gadget_disconnect() is done there. > >> > >>> drd_set_protocol(fsm, PROTO_UNDEF); > >>> otg_drv_vbus(otg, 0); > >>> break; > >>> case OTG_STATE_B_PERIPHERAL: > >>> drd_set_protocol(fsm, PROTO_GADGET); > >>> + usb_udc_vbus_handler(gadget, true); > >> > >> This is redundant as well since usb_gadget_start() is doing a > >> usb_gadget_connect(). > >> > >>> otg_drv_vbus(otg, 0); > >>> break; > >>> ...... > >>> }; > >>> > >>> } > >>> > >>> When the OTG FSM is added to this framework, it can keep > >>> usb_fsm->ops->loc_conn, and using the current FSM. > >>> > >> > >> I have no strong opinions for or against usb_fsm->ops->loc_conn. > >> Although strictly speaking, we shouldn't take any action based on loc_conn. > > > > Strictly speaking(OTG spec), all you does is for loc_conn, but you think > > it's start_gadget. > > > >> It is just a state variable indicator. > > > > Nobody check this "indicator". > > > > Of cos, this is not a big deal, you can define the new API as is, > > do udc_start() + gadget_connect() in one shot, it's up to user to > > decide if use your usb_otg_start_gadget(), in case of udc_start() > > followed by gadget_connect() is not wanted, user can/need do udc_start() > > and something else before do gadget_connect. > > Please don't get me wrong. I want the full OTG state machine to be able > to use usb_otg_start/stop_gadget(). > Sure, but you may change above APIs a little (delete usb_gadget_connect). -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
