Date:	Wed, 25 May 2016 15:21:39 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	<peter.chen@...escale.com>, <balbi@...nel.org>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>, <dan.j.williams@...el.com>,
	<mathias.nyman@...ux.intel.com>, <Joao.Pinto@...opsys.com>,
	<sergei.shtylyov@...entembedded.com>, <jun.li@...escale.com>,
	<grygorii.strashko@...com>, <yoshihiro.shimoda.uh@...esas.com>,
	<robh@...nel.org>, <nsekhar@...com>, <b-liu@...com>,
	<linux-usb@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v8 08/14] usb: otg: add OTG/dual-role core

On 25/05/16 05:44, Peter Chen wrote:
> On Tue, May 24, 2016 at 12:45:46PM +0300, Roger Quadros wrote:
>> Hi Peter,
>>
>> I have one question here. Please see below.
>>
>> On 13/05/16 13:03, Roger Quadros wrote:
>>> It provides APIs for the following tasks
>>>
>>> - Registering an OTG/dual-role capable controller
>>> - Registering Host and Gadget controllers to OTG core
>>> - Providing inputs to and kicking the OTG state machine
>>>
>>> Provide a dual-role device (DRD) state machine.
>>> DRD mode is a reduced functionality OTG mode. In this mode
>>> we don't support SRP, HNP and dynamic role-swap.
>>>
>>> In DRD operation, the controller mode (Host or Peripheral)
>>> is decided based on the ID pin status. Once a cable plug (Type-A
>>> or Type-B) is attached the controller selects the state
>>> and doesn't change till the cable in unplugged and a different
>>> cable type is inserted.
>>>
>>> As we don't need most of the complex OTG states and OTG timers
>>> we implement a lean DRD state machine in usb-otg.c.
>>> The DRD state machine is only interested in 2 hardware inputs
>>> 'id' and 'b_sess_vld'.
>>>
>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>> ---
>>>  drivers/usb/common/Makefile  |    2 +-
>>>  drivers/usb/common/usb-otg.c | 1042 ++++++++++++++++++++++++++++++++++++++++++
>>>  drivers/usb/core/Kconfig     |    4 +-
>>>  include/linux/usb/gadget.h   |    2 +
>>>  include/linux/usb/hcd.h      |    1 +
>>>  include/linux/usb/otg-fsm.h  |    7 +
>>>  include/linux/usb/otg.h      |  154 ++++++-
>>>  7 files changed, 1206 insertions(+), 6 deletions(-)
>>>  create mode 100644 drivers/usb/common/usb-otg.c
>>>
>>
>> <snip>
>>
>>> +
>>> +/**
>>> + * usb_otg_register() - Register the OTG/dual-role device to OTG core
>>> + * @dev: OTG/dual-role controller device.
>>> + * @config: OTG configuration.
>>> + *
>>> + * Registers the OTG/dual-role controller device with the USB OTG core.
>>> + *
>>> + * Return: struct usb_otg * if success, ERR_PTR() if error.
>>> + */
>>> +struct usb_otg *usb_otg_register(struct device *dev,
>>> +				 struct usb_otg_config *config)
>>> +{
>>> +	struct usb_otg *otg;
>>> +	struct otg_wait_data *wait;
>>> +	int ret = 0;
>>> +
>>> +	if (!dev || !config || !config->fsm_ops)
>>> +		return ERR_PTR(-EINVAL);
>>> +
>>> +	/* already in list? */
>>> +	mutex_lock(&otg_list_mutex);
>>> +	if (usb_otg_get_data(dev)) {
>>> +		dev_err(dev, "otg: %s: device already in otg list\n",
>>> +			__func__);
>>> +		ret = -EINVAL;
>>> +		goto unlock;
>>> +	}
>>> +
>>> +	/* allocate and add to list */
>>> +	otg = kzalloc(sizeof(*otg), GFP_KERNEL);
>>> +	if (!otg) {
>>> +		ret = -ENOMEM;
>>> +		goto unlock;
>>> +	}
>>> +
>>> +	otg->dev = dev;
>>> +	otg->caps = config->otg_caps;
>>
>> Here, we should be checking if user needs to disable any OTG features. So,
>>
>> 	if (dev->of_node)
>> 		of_usb_update_otg_caps(dev->of_node, &otg->caps);
>>
>> Do you agree?
>> This means we need to change otg->caps from 'struct usb_otg_caps *caps;'
>> to 'struct usb_otg_caps caps;' so that we can modify the local copy instead
>> of the one passed by the OTG controller.
> 
> Why can't modify the one from OTG controller directly?
> 

There are 2 things.
1) OTG features supported by hardware. This is the controller's config->otg_caps
2) OTG features needed by system designer. This can be a subset of (1).
This needs to be maintained in the OTG core, based on config->otg_caps and
device tree disable flags.

So we can't use OTG controller config->otg_caps directly.

>>
>> We can also move of_usb_update_otg_caps() to otg.h.
>>
>> We will also need to modify the udc-core code so that it sets gadget->otg_caps
>> to the modified otg_caps from the OTG core. This will ensure that the right
>> OTG descriptors are sent.
>>
>> So we will have to introduce an API.
>>
>> struct usb_otg_caps *usb_otg_get_otg_caps(struct device *otg_dev)
>>
>> And in udc-core.c,
>>
>> static int udc_bind_to_driver(struct usb_udc *udc, struct usb_gadget_driver *driver)
>> {
>> ..
>>         ret = driver->bind(udc->gadget, driver);
>>         if (ret)
>>                 goto err1;
>>
>>         /* If OTG, the otg core starts the UDC when needed */
>>         if (udc->gadget->otg_dev) {
>> +		udc->gadget->is_otg = true;
> 
> gadget->is_otg is only set to true if fully OTG is supported and it
> needs to send OTG descriptors at this case. DRD devices should not send OTG
> descriptors.

Agreed.

> 
>> +		udc->gadget->otg_caps = usb_otg_get_otg_caps(udc->gadget->otg_dev);
> 
> Getting otg capabilities should be prior to driver->bind since
> usb_otg_descriptor_init is called at that. Besides, Gadget driver

Correct.

> may be probed before otg driver is registered

udc_bind_to_driver gets called only when both, udc driver and function driver
are available. Defer probing will have to be done in usb_add_gadget_udc_release().

> 
> I am wonder if we can implement defer probe for gadget/udc/host driver
> if otg driver is not probed, in that case, some designs can be simpler
> like wait list in otg driver.

Agree with you on that. Should I work on implementing -EPROBE_DEFER for
hcd.c and udc-core.c if hcd/udc is meant for otg and OTG controller is not
yet probed?

--
cheers,
-roger

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