Date:	Thu, 19 Mar 2015 22:41:23 +0800
From:	Li Jun <b47624@...escale.com>
To:	Roger Quadros <rogerq@...com>
CC:	<gregkh@...uxfoundation.org>, <balbi@...com>,
	<stern@...land.harvard.edu>, <dan.j.williams@...el.com>,
	<peter.chen@...escale.com>, <jun.li@...escale.com>,
	<mathias.nyman@...ux.intel.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [RFC][PATCH 3/9] usb: otg: add OTG core

On Thu, Mar 19, 2015 at 12:30:46PM +0200, Roger Quadros wrote:
> On 19/03/15 10:26, Li Jun wrote:
> > On Wed, Mar 18, 2015 at 03:55:57PM +0200, Roger Quadros wrote:
> >> The OTG core instantiates the OTG Finite State Machine
> >> per OTG controller and manages starting/stopping the
> >> host and gadget controllers based on the bus state.
> >>
> >> It provides APIs for the following tasks
> >>
> >> - Registering an OTG capable controller
> >> - Registering Host and Gadget controllers to OTG core
> >> - Providing inputs to and kicking the OTG state machine
> >>
> >> TODO:
> >> - sysfs interface to allow application inputs to OTG state machine
> >> - otg class?
> >>
> >> Signed-off-by: Roger Quadros <rogerq@...com>
> >> ---
> >> +struct otg_data {
> >> +	struct device *dev;	/* HCD & GCD's parent device */
> >> +
> >> +	struct otg_fsm fsm;
> >> +	/* HCD, GCD and usb_otg_state are present in otg_fsm->otg
> >> +	 * HCD is bus_to_hcd(fsm->otg->host)
> >> +	 * GCD is fsm->otg->gadget
> >> +	 */
> >> +	struct otg_fsm_ops fsm_ops;	/* private copy for override */
> >> +	struct usb_otg otg;
> >> +	struct usb_hcd *shared_hcd;	/* if shared HCD registered */
> >> +
> >> +	/* saved hooks to OTG device */
> >> +	int (*start_host)(struct otg_fsm *fsm, int on);
> >> +	int (*start_gadget)(struct otg_fsm *fsm, int on);
> >> +
> >> +	struct list_head list;
> >> +
> >> +	struct work_struct work;	/* OTG FSM work */
> >> +	struct workqueue_struct *wq;
> >> +
> >> +	struct otg_timer timers[NUM_OTG_FSM_TIMERS];
> >> +
> >> +	bool fsm_running;
> >> +	bool gadget_can_start;		/* OTG FSM says gadget can start */
> >> +	bool host_can_start;		/* OTG FSM says host can start */
> > 
> > Do not understand above 2 *_can_start flags from the patch, which are set
> > only when you really start host/gadget, to prevent host/gadget driver to
> > start it out of otg fsm control?
> 
> host_can_start is used only by this driver in the following _unlikely_ condition
> and could probably be got rid of.
> - Primary HCD and gadget registers
> - OTG FSM signals host to start but it can't start as shared HCD isn't yet registered.
> so we set this flag.
> - when shared HCD registers, we check the flag and explicitly start both the host controllers.
> 
> gadget_can_start is used by the gadget driver through the usb_otg_gadget_can_start() API.
> This is needed because gadget might start at a later time depending on either
> - gadget function driver loads

I think it should be loaded before kick off OTG fsm.

> - userspace enables softconnect.

Why use the input of softconnect in userspace? I suppose all inputs should be
in scope/defined by OTG spec(a_bus_req, b_bus_req...).
So it's possible the gadget has not been started(pull up DP) while the OTG fsm
is in b_peripheral state? If yes, it's breaking OTG spec 7.2.3:
... 
When a high-speed capable B-device enters this state it shall enable its pull-up
on D+. After the B-device enables its pull-up, it shall monitor the state of the
bus to determine if a bus reset is being signaled by the A-device.
...

So for B-device, it should start gadget(pull up DP) if detects valid BSV vbus,
that's the only condition.

Li Jun
> 
> > 
> > Li Jun
> >> +
> >> +	/* use otg->fsm.lock for serializing access */
> >> +};
> >> +
> >> + * Can be called in IRQ context.
> >> + */
> >> +void usb_otg_sync_inputs(struct otg_fsm *fsm)
> >> +{
> >> +	struct otg_data *otgd = container_of(fsm, struct otg_data, fsm);
> >> +
> >> +	/* Don't kick FSM till it has started */
> >> +	if (!otgd->fsm_running)
> >> +		return;
> >> +
> >> +	/* Kick FSM */
> >> +	queue_work(otgd->wq, &otgd->work);
> >> +}
> >> +EXPORT_SYMBOL_GPL(usb_otg_sync_inputs);
> >> +
> >> +/**
> >> + * usb_otg_kick_fsm - Kick the OTG state machine
> >> + * @hcd_gcd_device:	Host/Gadget controller device
> >> + *
> >> + * Used by USB host/device stack to sync OTG related
> >> + * events to the OTG state machine.
> >> + * e.g. change in host_bus->b_hnp_enable, gadget->b_hnp_enable
> >> + *
> > There are quite a few otg fsm variables which should be updated when 
> > events/interrupts(b_conn, a_srp_det, ...) occur, how is your plan to
> > update them? Still rely on specific controller driver irq handler to
> > capture all those events and update them?
> 
> Yes, my plan was that the OTG controller driver will handle those
> interrupts, update otg_fsm members and call usb_otg_sync_inputs() to
> notify the OTG FSM.
> 
> cheers,
> -roger
> 
> > 
> > Li Jun
> >> + * Returns: 0 on success, error value otherwise.
> >> + */
> >> +int usb_otg_kick_fsm(struct device *hcd_gcd_device)
> >> +{
> >> +	struct otg_data *otgd;
> >> +
> >> +	mutex_lock(&otg_list_mutex);
> >> +	otgd = usb_otg_device_get_otgd(hcd_gcd_device->parent);
> >> +	if (!otgd) {
> >> +		dev_err(hcd_gcd_device, "%s: invalid host/gadget device\n",
> >> +			__func__);
> >> +		mutex_unlock(&otg_list_mutex);
> >> +		return -ENODEV;
> >> +	}
> >> +
> >> +	mutex_unlock(&otg_list_mutex);
> >> +	usb_otg_sync_inputs(&otgd->fsm);
> >> +
> >> +	return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(usb_otg_kick_fsm);
> >> -- 
> >> 2.1.0
> >>
> 
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