Hi, > From: Peter Chen > Sent: Wednesday, June 22, 2016 12:34 PM > > On Tue, Jun 21, 2016 at 05:47:47PM +0300, Felipe Balbi wrote: > > > > Hi, > > > > Peter Chen <hzpeterchen@xxxxxxxxx> writes: > > >> >> >> >> >>> + * @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. > > >> >> > > >> > > > >> > Since nxp SoC claims they are OTG compliance, we need to pass usb.org > > >> > test. The internal bsp has passed PET test, and formal compliance test > > >> > is on the way (should pass too). > > >> > > > >> > The dual-role and OTG compliance use the same zImage, but different > > >> > dtb. > > >> > > >> okay, that's good to know. Now, the question really is: considering we > > >> only have one user for this generic OTG FSM layer, do we really need to > > >> make it generic at all? I mean, just look at how invasive a change that > > >> is. > > > > > > If the chipidea is the only user for this roger's framework, I don't > > > think it is necessary. In fact, Roger introduces this framework, and > > > the first user is dwc3, we think it can be used for others. Let's > > > > Right, we need to look at the history of dwc3 to figure out why the > > conclusion that dwc3 needs this was made. > > > > Roger started working on this framework when Power on Reset section of > > databook had some details which weren't always clear and, for safety, we > > always had reset asserted for a really long time. It was so long (about > > 400 ms) that resetting dwc3 for each role swap was just too much. > > > > Coupled with that, the OTG chapter wasn't very clear either on > > expections from Host and Peripheral side initialization in OTG/DRD > > systems. > > > > More recent version of dwc3 databook have a much better description of > > how and which reset bits _must_ be asserted and which shouldn't be > > touched unless it's for debugging purposes. When I implemented that, our > > ->probe() went from 400ms down to about 50us. > > > > Coupled with that, the OTG chapter also became a lot clearer to the > > point that it states you just don't initialize anything other than the > > OTG block, and just wait for OTG interrupt to do whatever it is you need > > to do. > > > > This meant that we could actually afford to do full reinitialization of > > dwc3 on role swap (it's now only 50us anyway) and we knew how to swap > > roles properly. > > > > (The reason for needing soft-reset during role swap is kinda long. But > > in summary dwc3 shadows register writes to both host and peripheral > > sides) > > > > > just discuss if it is necessary for dual-role switch. > > > > fair. However, if we have a single user we don't have a Generic > > layer. There's not enough variance to come up with truly generic > > architecture for this. > > > > -- > > I have put some points in my last reply [1], I summery it here to > see if a generic framework is deserved or not? > > 1. If there are some parts we can use during the role switch > - The common start/stop host and peripheral operation > eg, when switch from host to peripheral, all drivers can use > usb_remove_hcd to finish it. > - A common workqueue to handle vbus and id event > - sysfs for role switch > > 2. Does a mux driver can do it well? Yoshihiro, here we need your > point. The main point is if we need to call USB API to change > roles (eg, usb_remove_hcd) during the role switch, thanks. In my platform, it doesn't need to call USB API (usb_remove_hcd) when "A-host" is changed to "A-peripheral". (Since this is a prototype local code, the code is not upstreaming yet though.) Best regards, Yoshihiro Shimoda > > [1] http://www.spinics.net/lists/linux-usb/msg142974.html > -- > > 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
