Date: Wed, 22 Apr 2015 10:17:24 +0800
From: Peter Chen <peter.chen@freescale.com>
To: Roger Quadros <rogerq@ti.com>
CC: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "balbi@ti.com" <balbi@ti.com>,
        "stern@rowland.harvard.edu" <stern@rowland.harvard.edu>,
        "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
        "Jun.Li@freescale.com" <Jun.Li@freescale.com>,
        "mathias.nyman@linux.intel.com" <mathias.nyman@linux.intel.com>,
        "tony@atomide.com" <tony@atomide.com>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
        "macpaul@gmail.com" <macpaul@gmail.com>
Subject: Re: [RFC][PATCH v2 00/13] USB: OTG/DRD Core functionality
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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

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.

> 
> > - 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.

> 
> > - 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?
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 */
> 
> 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?

> > 
> > 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
> 

-- 

Best Regards,
Peter Chen
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