Re: [PATCH v4 07/13] usb: otg: add OTG core

[Roger Quadros <rogerq@ti.com>]

On 09/09/15 11:45, Peter Chen wrote:
> On Wed, Sep 09, 2015 at 12:33:20PM +0300, Roger Quadros wrote:
>> On 09/09/15 11:13, Peter Chen wrote:
>>> On Wed, Sep 09, 2015 at 12:08:10PM +0300, Roger Quadros wrote:
>>>> On 09/09/15 05:21, Peter Chen wrote:
>>>>> On Tue, Sep 08, 2015 at 03:25:25PM +0300, Roger Quadros wrote:
>>>>>>
>>>>>>
>>>>>> On 08/09/15 11:31, Peter Chen wrote:
>>>>>>> On Mon, Sep 07, 2015 at 01:23:01PM +0300, Roger Quadros wrote:
>>>>>>>> On 07/09/15 04:23, Peter Chen wrote:
>>>>>>>>> On Mon, Aug 24, 2015 at 04:21:18PM +0300, Roger Quadros wrote:
>>>>>>>>>> + * This is used by the USB Host stack to register the Host controller
>>>>>>>>>> + * to the OTG core. Host controller must not be started by the
>>>>>>>>>> + * caller as it is left upto the OTG state machine to do so.
>>>>>>>>>> + *
>>>>>>>>>> + * Returns: 0 on success, error value otherwise.
>>>>>>>>>> + */
>>>>>>>>>> +int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
>>>>>>>>>> +			 unsigned long irqflags, struct otg_hcd_ops *ops)
>>>>>>>>>> +{
>>>>>>>>>> +	struct usb_otg *otgd;
>>>>>>>>>> +	struct device *hcd_dev = hcd->self.controller;
>>>>>>>>>> +	struct device *otg_dev = usb_otg_get_device(hcd_dev);
>>>>>>>>>> +
>>>>>>>>>
>>>>>>>>> One big problem here is: there are two designs for current (IP) driver
>>>>>>>>> code, one creates dedicated hcd device as roothub's parent, like dwc3.
>>>>>>>>> Another one doesn't do this, roothub's parent is core device (or otg device
>>>>>>>>> in your patch), like chipidea and dwc2.
>>>>>>>>>
>>>>>>>>> Then, otg_dev will be glue layer device for chipidea after that.
>>>>>>>>
>>>>>>>> OK. Let's add a way for the otg controller driver to provide the host and gadget
>>>>>>>> information to the otg core for such devices like chipidea and dwc2.
>>>>>>>>
>>>>>>>
>>>>>>> Roger, not only chipidea and dwc2, I think the musb uses the same
>>>>>>> hierarchy. If the host, device, and otg share the same register
>>>>>>> region, host part can't be a platform driver since we don't want
>>>>>>> to remap the same register region again.
>>>>>>>
>>>>>>> So, in the design, we may need to consider both situations, one
>>>>>>> is otg/host/device has its own register region, and host is a
>>>>>>> separate platform device (A), the other is three parts share the
>>>>>>> same register region, there is only one platform driver (B).
>>>>>>>
>>>>>>> A:
>>>>>>>
>>>>>>> 			IP core device 
>>>>>>> 			    |
>>>>>>> 			    |
>>>>>>> 		      |-----|-----|
>>>>>>> 		      gadget   host platform device	
>>>>>>> 		      		|
>>>>>>> 				roothub
>>>>>>>
>>>>>>> B:
>>>>>>>
>>>>>>> 			IP core device
>>>>>>> 			    |
>>>>>>> 			    |
>>>>>>> 		      |-----|-----|
>>>>>>> 		      gadget   	 roothub
>>>>>>> 		      		
>>>>>>>
>>>>>>>> This API must be called before the hcd/gadget-driver is added so that the otg
>>>>>>>> core knows it's linked to an OTG controller.
>>>>>>>>
>>>>>>>> Any better idea?
>>>>>>>>
>>>>>>>
>>>>>>> A flag stands for this hcd controller is the same with otg controller
>>>>>>> can be used, this flag can be stored at struct usb_otg_config.
>>>>>>
>>>>>> What if there is another architecture like so?
>>>>>>
>>>>>> C:
>>>>>> 			[Parent]
>>>>>> 			   |
>>>>>> 			   |
>>>>>> 		|------------------|--------------|
>>>>>> 	[OTG core]		[gadget]	[host]
>>>>>>
>>>>>> We need a more flexible mechanism to link the gadget and
>>>>>> host device to the otg core for non DT case.
>>>>>>
>>>>>> How about adding struct usb_otg parameter to usb_otg_register_hcd()?
>>>>>>
>>>>>> e.g.
>>>>>> int usb_otg_register_hcd(struct usb_otg *otg, struct usb_hcd *hcd, ..)
>>>>>>
>>>>>> If otg is NULL it will try DT otg-controller property or parent to
>>>>>> get the otg controller.
>>>>>
>>>>> How usb_otg_register_hcd get struct usb_otg, from where?
>>>>
>>>> This only works when the parent driver creating the hcd has registered the
>>>> otg controller too.
>>>>
>>>
>>> Sorry? So we need to find another way to solve this issue, right?
>>
>> For existing cases this is sufficient.
>> The otg device is either the one supplied during usb_otg_register_hcd
>> (cases B and C) or it is the parent device (case A).
> 
> How we differentiate case A and case B at usb_otg_register_hcd?
> Would you show me the sample code?

Case A:

hcd platform driver doesn't know about otg device so it calls

	usb_add_hcd(hcd,..)->usb_otg_register_hcd(NULL, hcd,..);

Case B:

core driver knows about both otg and hcd so it calls
	usb_otg_register_hcd(otg, hcd,...);

code:

usb_otg_register_hcd(struct usb_otg *otg, struct usb_hcd *hcd, ...)
{
	if (!otg) {
		struct device *otg_dev;
		struct device *hcd_dev = hcd->self.controller;

		/* first get otg device */
		if (hcd_dev->of_node) { /* DT */
			struct device_node *np;
			struct platform_device *pdev;

			/* get otg from otg-controller property */
			np = of_parse_phandle(hcd_dev->of_node, "otg-controller",
					      0);
			pdev = of_find_device_by_node(np);
			of_node_put(np);
			if (!pdev) {
				dev_err(&pdev->dev, "couldn't get otg-controller device\n");
				return -EINVAL;
			}

			otg_dev = &pdev->dev;
		} else {
			/* Assume otg dev is parent */
			otg_dev = hcd_dev->parent;
		}

		otg = usb_otg_get_data(otg_dev);
		if (!otg) {
			/* otg controller not registered */
			return -EVINVAL
		}
	} else {
		/* use otg as is */
	}
}

usb_otg_get_data() returns the usb_otg structure if it finds a matching
otg_dev in the otg_dev list.

For this to work otg controller _must_ register before hcd/gadget.

> 
>>
>> It does not work when the 3 devices are totally independent and get registered
>> at different times.
>> I don't think there is such a case for non-DT yet, but let's not have this
>> limitation. So yes, we need to look for better solution :).
>>
> 
> Yes, we need to find some places to store gadget/host/otg information,
> Alan's suggestion to save them at device drvdata may be a direction, but
> I still doesn't have way to cover all cases.
> 

Yes, let's discuss more in that direction.

--
cheers,
-roger