On Mon, 16 Jun 2014, Peter Chen wrote: > On Fri, Jun 13, 2014 at 10:19:36AM -0400, Alan Stern wrote: > > On Fri, 13 Jun 2014, Peter Chen wrote: > > > > > OK, we can keep our g_xxx gadget driver just support the basic feature. But > > > the bug that causes gadget driver load fail due to udc is probed deferral should > > > be fixed, do you think so, we can't wait until configfs has total been ready. > > > > That problem has always existed. There never has been a time when a > > gadget driver could be loaded before the UDC driver was ready. Does it > > really need to be fixed now? > > > > Yes, otherwise, the device which the udc is probed deferral and the > gadget driver is build-in will never work. If we skip fixing it, this > problem will exist for more than 2 years, it is too long. > > I have a support request from android team that usb peripheral function > never works from 3.10.x kernel at one device, I think it is a common problem, > no only I meet it. > > Below are links which this problem reports: > > http://marc.info/?l=linux-usb&m=139380872501745&w=2 > http://marc.info/?l=linux-usb&m=137706435611447&w=2 > > > If you do want to fix the problem, there's a much easier way than what > > you posted. See below. > > > Robert Baldyga posts the similar solution, but seems Felipe doesn't > agree it. > http://www.spinics.net/lists/linux-usb/msg102795.html > > Then, you and Felipe has a discussion for this problem: > http://www.spinics.net/lists/linux-usb/msg106760.html Okay, I get it. Felipe didn't want to do this because you might end up loading a gadget driver that never gets bound. There might not even be any UDC devices at all. Felipe, I think the problem of having unbound gadget drivers isn't so bad. It's just like having unbound drivers of any sort. For example, the Fedora kernels have ohci-hcd and uhci-hcd built-in. Relatively few systems have both OHCI and UHCI controllers (lots of current machines have neither); everybody else ends up with at least one unused driver and no way to remove it. If Fedora can do this, I think we can allow users to have unnecessary gadget drivers. In fact, I don't know of any other kind of driver module whose init routine will fail if there's no hardware to bind to. I suggest you go ahead and accept Robert Baldyga's original patch -- except for one little problem: The patch forgets to add driver->list to the global driver_list if the driver gets bound immediately. The list_add_tail(&driver->list, &driver_list); call needs to be moved up near the start of usb_gadget_probe_driver(). Alan Stern -- 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
