Hi, Peter Chen <hzpeterchen@xxxxxxxxx> writes: >> 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? to avoid confusion with the terminology, yes. With that settled, let's figure out how you can deliver what your marketting guys are asking of you. >> > 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. okay, thanks -- balbi
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