On Mon, Mar 27, 2017 at 02:53:27PM +0200, Moreno Bartalucci wrote: > > Il giorno 25 mar 2017, alle ore 08:21, Lars Melin <larsm17@xxxxxxxxx> ha scritto: > > > >> > >> The usb device has been disconnected, why it still cares about VBUS > >> power? > > > > Morphing devices (3G dongles, wifi dongles, some printers) boots up in install mode, usually only as a virtual cd-rom containing Windows drivers and software. > > [...] > > why a host only configured port should cut the VBUS supply, it could be always on right? > > > > Yes, that’s exactly the problem I tried to solve with this patch. Yeah, the problem is clear to me now. > I have to add that the problem was not there with kernels up to > 4.8.17, I started to see it with 4.9 and up. > > By git-bisecting kernel sources, it appears this behaviour has been > introduced by this commit: > > 2f3fd2c5bde1f94513c3dc311ae64494085ec371 It seems this patch changes how OTG_STATE_A_WAIT_VRISE and OTG_STATE_A_WAIT_BCON are used. > > I also agree that, in my opinion, a host only port should never remove > the VBUS supply, as it happens on all the PCs (linux+windows+mac) that > I tested until now. True. It is just that the musb driver handles both dual-role and host-only mode. > > I saw this problem on a beaglebone black. Of course I’m available to > do all the tests that you might suggest me to help you better > understand the issue. Thanks for the offer. Please let me look at the problem first, I have a modem to test. It is not clear why the original driver clears VBUS in this place, so I have to ensure your patch is the correct change. Regards, -Bin. -- 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
