Message-ID: <55379738.1090808@ti.com>
Date:	Wed, 22 Apr 2015 15:42:32 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <peter.chen@...escale.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"balbi@...com" <balbi@...com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"Jun.Li@...escale.com" <Jun.Li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"macpaul@...il.com" <macpaul@...il.com>
Subject: Re: [RFC][PATCH v2 00/13] USB: OTG/DRD Core functionality

On 22/04/15 12:22, Peter Chen wrote:
> On Wed, Apr 22, 2015 at 10:33:24AM +0300, Roger Quadros wrote:
>> On 22/04/15 05:17, Peter Chen wrote:
>>> On Tue, Apr 21, 2015 at 10:34:01AM +0300, Roger Quadros wrote:
>>>> On 21/04/15 09:04, Peter Chen wrote:
>>>>>  
>>>>>>
>>>>>> On 20/04/15 06:05, Peter Chen wrote:
>>>>>>> On Tue, Apr 14, 2015 at 01:41:47PM +0300, Roger Quadros wrote:
>>>>>>>> This is an attempt to centralize OTG/Dual-role functionality in the kernel.
>>>>>>>> As of now I've got Dual-role functionality working pretty reliably on
>>>>>>>> dra7-evm. xhci side of things for OTG/DRD use are fixed in
>>>>>>>> http://thread.gmane.org/gmane.linux.kernel/1923161
>>>>>>>
>>>>>>> Hi Roger,
>>>>>>>
>>>>>>> Currently, there are two main problems for DRD/OTG framework.
>>>>>>>
>>>>>>> - For multi-platform supports, we may define CONFIG_USB_OTG, but the
>>>>>>> gadget should not add its otg descriptor to its configuration
>>>>>>> descriptors if it does not support one of otg features (SRP/HNP/ADP).
>>>>>>> Macpaul Lin's patch set [1] is the right way to do it.
>>>>>>
>>>>>> Agreed. That check (whether OTG descriptor can be added and which version
>>>>>> of it) has to be done at runtime and it must be added only if hardware supports
>>>>>> OTG _and_ kernel OTG support is enabled.
>>>>>>
>>>>>
>>>>> Ok, let's put this patch set in mainline first, since your patch set may need some
>>>>> information from it.
>>>>>  
>>>>>>> - We are lack of framework to handle OTG (DRD) switch, it is great you
>>>>>>> are designing it. The main problem for this framework is how to handle
>>>>>>> DRD/OTG FSM unify. My thought is we add two paths for them separate.
>>>>>>> For easy, I suggest if the platform supports one of otg features, then
>>>>>>> it goes to fully otg fsm, else it goes to simply otg fsm (like your
>>>>>>> drd fsm). If you agree with it too, you may not need to add another
>>>>>> "dr_mode"
>>>>>>> value.
>>>>>>
>>>>>> It would be nice that way but unfortunately it does't work in all cases.
>>>>>> e.g. What if the SoC itself supports all OTG features but the board is not
>>>>>> designed for OTG. Or the product designer simply is not interested in full OTG
>>>>>> support but just dual-role. So we need some flexibility for the device
>>>>>> tree/platform-data to specify that. This is where a new "dr_mode" == "dual-
>>>>>> role" is needed.
>>>>>>
>>>>>
>>>>> Since "dr_mode" has been widely used now, if we add a new property for it,  we
>>>>> need to change all drivers.
>>>>>
>>>>> Your OTG/DRD framework needs to (partial) use otg fsm, and we will not teach old
>>>>> driver to use it since there are some driver related stuffs.
>>>>
>>>> fair enough. Let's not change dr_mode then and decide based on other parameters.
>>>>
>>>>>
>>>>> SRP/HNP/ADP support can be board level capabilities, and we may consider the
>>>>> otg device which does not support otg fsm (hardware finishes fsm). So I suggest
>>>>> we have below properties at dts:
>>>>>
>>>>> - otg-support /* fully otg support */
>>>>> - otg-fsm-support /* fully otg fsm support */
>>>>
>>>> what is the difference between otg-support and otg-fsm-support?
>>>
>>> Like I mentioned at above, the hardware finishes HNP/SRP which does not
>>> use otg fsm code (usb-otg-fsm.c), most of legacy otg platforms (musb?)
>>> use this way, for these platforms, only need to set otg-support = 1
>>
>> So dr_mode = "otg" _and_ otg-support = 1?
>>
> 
> Yes
> 
>> Again wouldn't this involve changes to dts for musb like platforms
>> supporting full OTG?
>>
>> Instead we could add a new field saying otg-fsm-type
>> "otg-hw", "otg-sw", "drd-sw"
>>
>> If the field is absent it defaults to "otg-hw".
>> This also means we don't need otg-fsm-support flag.
>>
> 
> Yes, that's we doesn't need to change for old platforms, but
> we keep our default value as small possibilities, most of current
> platforms are only drd platform, it is hard choice.
> 
> My original thought was nothing need to add at dts for drd device.
> 
>> Now the pseudo-code to decide fsm is
>>
>> if (dr_mode == "otg" && CONFIG_USB_OTG)
>> 	if (otg-fsm-type == "otg-sw") {
>> 		if (CONFIG_USB_OTG_FSM)
>> 			full otg fsm support via sw
>> 		else
>> 			error "CONFIG_USB_OTG_FSM" not set
>> 	} else if (otg-fsm-type == "drd-sw") {
>> 		dual role fsm support
>> 	} else {
>> 		full otg support via hw
>> 	}
>>
>> 	if (otg-fsm-type == "otg
>> else
>> 	error "CONFIG_USB_OTG" not set
> 
> So we will have a separate drd fsm file, and the CONFIG_USB_OTG
> and CONFIG_USB_OTG_FSM are not needed to be defined, right?
> 

for drd case CONFIG_USB_OTG_FSM is definitely not needed.
I'm not sure if we can operate dual-role without CONFIG_USB_OTG.
I was thinking of combining the OTG core functionality (drivers/usb/common/usb-otg.c)
with CONFIG_USB_OTG.

>>
>>>
>>> For platforms which software finishes HNP/SRP using otg fsm code, need
>>> to set both flags.
>>>
>>> For platforms which only do role switch through id pin, do not need to
>>> set both.
>>>
>>
>> OK. I get it now.
>>
>>>>
>>>>> - otg-ver /* eh & otg supplement version */
>>>>
>>>> we can get otg version from the OTG controller. What exactly is the
>>>> otg-ver in dts for?
>>>
>>> Since most of otg stuffs are software's, eg, for otg descriptor, we will
>>> only use otg 2.0 descriptor when both CONFIG_USB_OTG20 and otg-ver = 20
>>> are set.
>>
>> CONFIG_USB_OTG20 is redundant now. Plus I mentioned in the respective thread
>> that it is not suitable for booting single image on different platforms.
>>
> 
> Ok, agree. Then we need to define two usb otg descriptors
> for both 1.3 and 2.0, and we need to have two otg descriptor array
> at gadget driver. And the code at gadget driver will like below:
> 
> static const struct usb_descriptor_header *otg_desc_13[] = {
> 	(struct usb_descriptor_header *) &(struct usb_otg_descriptor_13){
> 		.bLength =		sizeof(struct usb_otg_descriptor_13),
> 		.bDescriptorType =	USB_DT_OTG,
> 
> 		/*
> 		 * REVISIT SRP-only hardware is possible, although
> 		 * it would not be called "OTG" ...
> 		 */
> 		.bmAttributes =		USB_OTG_SRP | USB_OTG_HNP,
> 	},
> 	NULL,
> };
> 
> static const struct usb_descriptor_header *otg_desc_20[] = {
> 	(struct usb_descriptor_header *) &(struct usb_otg_descriptor_20){
> 		.bLength =		sizeof(struct usb_otg_descriptor_20),
> 		.bDescriptorType =	USB_DT_OTG,
> 
> 		/*
> 		 * REVISIT SRP-only hardware is possible, although
> 		 * it would not be called "OTG" ...
> 		 */
> 		.bmAttributes =		USB_OTG_SRP | USB_OTG_HNP,
> 		.bcdOTG =               cpu_to_le16(0x0200),
> 	},
> 	NULL,
> };

instead of hardcoding bmAttributes field, it must be obtained from the
appropriate data structure that was set by the controller driver
by reading DT and OTG hardware info.

> 
> During bind process:
> 
> 	if (gadget_is_otg_13(c->cdev->gadget))
> 		c->descriptors = otg_desc_13;
> 	else if (gadget_is_otg_20(c->cdev->gadget))
> 		c->descriptors = otg_desc_20;

Probably a helper utitily can do the necessary checks and build the
otg descriptor for us.
		usb_otg_get_descriptor(c->descriptors);

e.g. for OTG3.0 we have a new flag USB_OTG_RSP, and this helper
can be upgraded in the future.

> 
>> As of now I can see 2 inputs regarding otg-ver
>> - One comes from otg-ver DT property or platform data.
>> - Second that may come from OTG controller registers. e.g. It might support
>> OTG v3.0 but system designer wants to limit to OTG v2.0 via otg-ver.
>>
>> Controller driver can decide among the 2 and set the appropriate otg version
>> in the data structure.
>>
> 
> Yes, it is the same we do for usb mode.

OK.

cheers,
-roger

> 
>>>
>>>>
>>>>> - adp-support /* board adp support */ 
>>>>> - srp-support /* board srp support */
>>>>> - hnp-support /* board hnp support */
>>>>
>>>> So if these options are not provided in DTS but the OTG core supports them then
>>>> we keep the respective feature disabled?
>>>
>>> Yes.
>>>
>>>> Won't this need dts change for existing boards?
>>>
>>> Does you know any dts based platform supports hnp/srp?
>>
>> I'm the wrong person to ask this. Maybe Felipe/Tony can comment.
>> Irrespective of whether any dts platforms supports hsn/srp or not
>> we must assume that till date dr_mode = otg implies full otg support
>> and we cannot change its meaning.
>>
>> We can add new fields to indicate dual-role mode which is a new feature.
> 
>>
>>> For chipidea platform, currently, we depends on kernel
>>> configurations (CONFIG_USB_OTG_FSM), but it is incorrect way.
>>>
>>>>
>>>> Instead how about having disable flags instead.
>>>>  - adp-disable	/* board doesn't support adp */
>>>>  - srp-disable	/* board doesn't support srp */
>>>>  - hnp-disable	/* board doesn't support hnp */
>>>>
> 
> Like I mentioned above, it depends on which otg features we would like
> to give as default features for dual-role device.
> 
> For switching the role through the ID pin devices, we doesn't need any otg
> features.
> For adp/srp/hnp supported devices, we need (partial) otg features, and
> the fsm (hardware or software) are needed.
> 
>>>> Now, if the flags are not provided in dts we use the OTG core's flags.
>>>>
>>>
>>> How the OTG core's know if it supports these?
>>
>> By OTG core, I meant OTG controller core. At least the dwc3 OTG controller has
>> register bits to identify if it supports adp/srp/hnp.
>>
>> But we also need to keep in mind that adp feature can be provided separately even
>> if the OTG controller core doesn't support it.
>>
>> cheers,
>> -roger
>>
>>>
>>>>>
>>>>> Currently, if CONFIG_USB_OTG and CONFIG_USB_OTG_FSM are enabled, we will
>>>>> have otg fsm code (usb-otg-fsm.c).
>>>>>
>>>>> if (otg-support & otg-fsm-support)
>>>>> 	this device has fully otg support, and will follow full otg fsm transitions. 
>>>>> else
>>>>> 	this device is drd, and will follow simple otg fsm transtions. 
>>>>>
>>>>
>>>> cheers,
>>>> -roger
>>>>
>>>
>>
> 

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