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. > 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 ;-) -- balbi
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