> From: "Greg KH" <greg@xxxxxxxxx> > On Tue, Feb 07, 2017 at 06:56:20PM +0100, John Skelton wrote: > > > From: "Felipe Balbi" <felipe.balbi@xxxxxxxxxxxxxxx> > > > > I'm particularly interested in drivers/usb/core/config.c > > > > which appears to enforce the USB specification by refusing to allow a > > > > low speed CDC ACM. (Comment "Some buggy low-speed devices ...", at > > > > about line 300.) > > > > > > > > However, such devices exist and some are potentially quite useful (such > > > > as Arduinos & digistump). Various people have posted about not being > > > > able to use them with Linux and I think the above file is the reason > > > > (another well known OS family allows them). > > > > > > Here's the comment: > > > > > > /* Some buggy low-speed devices have Bulk endpoints, which is > > > * explicitly forbidden by the USB spec. In an attempt to make > > > * them usable, we will try treating them as Interrupt endpoints. > > > */ > > > > > > The code isn't forbidding CDC ACM low speed devices, it's forbidding > > > Bulk endpoints on Low speed, which don't exist :-) Are you saying there > > > are Bulk endpoints on low speed Arduinos? > > > > Yes - or I may have misunderstood the situation. > > > > It is code which is derived from V-USB > > https://www.obdev.at/products/vusb/index.html > > and is described at > > http://www.recursion.jp/prose/avrcdc/cdc-232.html > > > > If it worked with Linux it would be a handy way to provide output (such as > > debug data) from low-cost Arduinos and such like via USB. > > > > To be clear: I am not saying the Linux USB code is wrong. But it would > > be good to have a way to have the above kind of code work, such that > > screen / minicom etc can be used with it. > > > > That page says that any kernel newer than 2.6.31 should work just fine, > have you tried this out and had it fail? It does say that but it does not work. I get the dev_warn message that it has changed the Bulk endpoint to Interrupt but that's it. > For Windows, you note that you have to patch it. Remember, this is a > spec violation, you really shouldn't be doing this :) I'm not wanting to use Windows. Never again, if I can help it! John -- 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
