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Date: Wed, 25 May 2016 10:44:27 +0800
From: Peter Chen <hzpeterchen@gmail.com>
To: Roger Quadros <rogerq@ti.com>
Cc: peter.chen@freescale.com, balbi@kernel.org, tony@atomide.com,
        gregkh@linuxfoundation.org, dan.j.williams@intel.com,
        mathias.nyman@linux.intel.com, Joao.Pinto@synopsys.com,
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        grygorii.strashko@ti.com, yoshihiro.shimoda.uh@renesas.com,
        robh@kernel.org, nsekhar@ti.com, b-liu@ti.com,
        linux-usb@vger.kernel.org, linux-omap@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v8 08/14] usb: otg: add OTG/dual-role core
Message-ID: <20160525024427.GA31142@shlinux2>
References: <1463133808-10630-1-git-send-email-rogerq@ti.com>
 <1463133808-10630-9-git-send-email-rogerq@ti.com>
 <574422CA.8080002@ti.com>
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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@ti.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?

> 
> 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.

> +		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
may be probed before otg driver is registered

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.

>                 mutex_unlock(&udc_lock);
>                 usb_otg_register_gadget(udc->gadget, &otg_gadget_intf);
>                 mutex_lock(&udc_lock);
>         } else {
>                 ret = usb_gadget_udc_start(udc);
>                 if (ret) {
>                         driver->unbind(udc->gadget);
>                         goto err1;
>                 }
>                 usb_udc_connect_control(udc);
>         }
> ..
> }
> 
> What do you say?
> 
> regards,
> -roger
> --
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-- 

Best Regards,
Peter Chen