On Wed, Jun 22, 2016 at 09:51:19AM +0300, Felipe Balbi wrote: > > Hi, > > Peter Chen <hzpeterchen@xxxxxxxxx> writes: > >> >> >> > 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 UDC such as dwc3 already implements start/stop for peripheral and > host. Why would go through and indirection layer that just comes back to > us? (well, dwc3's host side, start/stop translates to adding/removing > xhci-plat's device) > > > - A common workqueue to handle vbus and id event > > I already have a threaded IRQ handler. Why do I need a workqueue? > I know it can be done in individual driver, don't you think we need a common part to manage the dual-role switch process, since dual-role switch is used more and more common, and there are so many switch methods: - ID pin - sysfs - type-c - OTG FSM - Registers Maybe Roger's framework is a little complicated, but if it is the correct direction, we can improve it. > > - sysfs for role switch > > A generic sysfs is desirable, but I really don't know where to put it. > Maybe it's enough to go down the hwmon route and just have an agreement > of filename and contents to be written to. > > -- > balbi -- 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
