On Mon, Jun 20, 2016 at 03:03:37PM +0300, Felipe Balbi wrote: > > Hi, > > >>> + > >>> + /* 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. > >>> + * @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. You are right, if the connector is type-c, it will be called as "type-c port" by people :) -- 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
