Re: To otg-fsm or not to otg-fsm? That is the question.

[Peter Chen <peter.chen@freescale.com>]

On Tue, Aug 12, 2014 at 09:13:47AM -0700, Tim Bird wrote:
> On Mon, Aug 11, 2014 at 5:28 PM, Peter Chen <Peter.Chen@freescale.com> wrote:
> > The OTG FSM at /usb/common/usb-otg-fsm.c is a software OTG FSM implementation
> > which follows On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification
> > (Revision 2.0 version 1.1a) Chapter 7 State Diagrams.
> >
> > If the platform doesn't support hardware otg fsm, it should follow above fsm implementation since
> > it follows the newest OTG & EH spec. Besides, as far as I know, the qualcomm uses
> > chipidea core for its usb2, then it should be easy for qualcomm using this common
> > otg fsm implementation.
> 
> OK.  sounds good.
> 
> Yes, the qualcomm chips use a chipidea core for usb2.  The main
> difficulty, IMHO, will
> be mapping the qcom charger state machine onto the generic OTG state
> machine implementation
> in usb-otg-fsm.  I'm not sure if I'll be able to embed the needed
> functionality into the existing functions
> called by the generic state machine, or if I'll need to add some new
> entries to the function table
> to handle this extra logic.
> 
> I'll probably try to get the driver working without the charger stuff
> first, and then, once I have a
> better idea of how the state machines map, try adding the charger
> stuff.  If I feel like I need
> to modify the generic state machine, I'll ask on list.  I'm a newbie
> at USB stuff and I don't want
> to break anything.
> 
> Thanks.
> 

One remind, you may need to know which role-switch function you need,
if you only need role-switch based in ID pin, then no OTG FSM support
is needed, this is current most of "OTG" device supports, it is not fully
OTG compliance.

-- 
Best Regards,
Peter Chen