On Tue, Jun 21, 2016 at 10:19:32AM +0300, Felipe Balbi wrote: > > Hi, > > Peter Chen <hzpeterchen@xxxxxxxxx> writes: > >> >>> + > >> >>> + /* start host */ > >> >>> + ret = hcd_ops->add(otg->primary_hcd.hcd, > >> >>> + otg->primary_hcd.irqnum, > >> >>> + otg->primary_hcd.irqflags); > >> >> > >> >> this is usb_add_hcd(), is it not? Why add an indirection? > >> > > >> > I've introduced the host and gadget ops interface to get around the > >> > circular dependency issue we can't avoid. > >> > otg needs to call host/gadget functions and host/gadget also needs to > >> > call otg functions. > >> > >> IMO, this shows a fragility of your design. You're, now, lying to > >> usb_hcd and usb_udc and making them register into a virtual layer that > >> doesn't exist. And that layer will end up calling the real registration > >> function when some magic event happens. > >> > >> This is only really needed for quirky devices like dwc3 (but see more on > >> dwc3 below) where host and peripheral registers shadow each > >> other. Otherwise we would be able to always keep hcd and udc always > >> registered. They would get different interrupt statuses anyway and > >> nothing would ever break. > >> > >> However, when it comes to dwc3, we already have all the code necessary > >> to workaround this issue by destroying the XHCI pdev when OTG interrupt > >> says we should be peripheral (and vice-versa). DWC3 also keeps track of > >> the OTG states for those folks who really care about OTG (Hint: nobody > >> has cared for the past 10 years, why would they do so now?) and we don't > >> need a SW state machine when the HW handles that for us, right? > >> > >> As for chipidea, IIRC, that doesn't need a SW state machine either, but > >> I know very little about that IP and don't even have documentation on > >> it. My understanding, however, is that chipidea behaves kinda like MUSB, > >> which changes roles automatically in HW based on ID pin state. > > > > Chipidea needs to set register for USB role manually. > > okay, so chipidea has private control of role. Much like dwc3. That's good. > > >> >>> + * @otg_dev: OTG controller device, if needs to be used with OTG core. > >> >> > >> >> do you really know of any platform which has a separate OTG controller? > >> >> > >> > > >> > Andrew had pointed out in [1] that Tegra210 has separate blocks for OTG, host > >> > and gadget. > >> > > >> > [1] http://article.gmane.org/gmane.linux.ports.tegra/22969 > >> > >> that's not an OTG controller, it's just a mux. No different than Intel's > >> mux for swapping between XHCI and peripheral-only DWC3. > >> > >> frankly, I would NEVER talk about OTG when type-C comes into play. They > >> are two competing standards and, apparently, type-C is winning when it > >> comes to role-swapping. > >> > > > > In fact, OTG is mis-used by people. Currently, if the port is dual-role, > > It will be considered as an OTG port. > > That's because "dual-role" is a non-standard OTG. Seen as people really > didn't care about OTG, we (linux-usb folks) ended up naturally referring > to "non-standard OTG" as "dual-role". Just to avoid confusion. So, unless we use OTG FSM defined in OTG spec, we should not mention "OTG" in Linux, right? > > > You are right, if the connector is type-c, it will be called as "type-c > > port" by people :) > > oh no, that's not what I'm talking about. If you read Type-C and PD > specs, they define their own method for data role swapping. USB OTG > doesn't fit on top of a Type-C environment. It's not about what people > will call it, it's really that OTG can't work on top of type-c. For > starters, there's no ID pin ;-) I know type-c, yes, there is no relationship between OTG and type-c. -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
