linux-kernel - Re: [RFC][PATCH 3/9] usb: otg: add OTG core

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Message-ID: <550AA556.1030301@ti.com>
Date:	Thu, 19 Mar 2015 12:30:46 +0200
From:	Roger Quadros <rogerq@...com>
To:	Li Jun <b47624@...escale.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 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
- userspace enables softconnect.

> 
> 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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