On Tuesday 05 March 2013 11:07:05 Bjørn Mork wrote: > "Fangxiaozhi (Franko)" <fangxiaozhi@xxxxxxxxxx> writes: > > > ------ commit 200e0d99 and commit cd060956, only put the switch > > command into kernel, instead of userspace usb_modeswitch utility. > > Yes. And that is the problem. It was agreed years ago that this > functionality belongs in userspace. Ref e.g > https://lkml.org/lkml/2009/12/15/332 > https://lkml.org/lkml/2010/4/19/216 > https://lkml.org/lkml/2012/2/28/569 > > Please note the re-occurrence of this discussion, despite the fact that > Matthew's message from 2009 should be quite clear. Since 2009 the facts have been changing. Basically we are encountering two trends 1. Power save has become more important 2. We are seeing devices that are switchable, yet include interfaces other than communication and virtual storage, foremost real storage in the form of a microSD-reader Whenever we cut power to a switchable device it reverts to the power-on state. That involves not only the communication functionality (which we could live with, as it cannot handle loss of power anyway) but also other interfaces. In addition we need to deal with resets which may or may not make the device revert to power-on This is a basic problem of the design. If you want reset_resume() for power loss to work you need to do it in kernel space for the same reason we restore the configuration in kernel space before we rebind the drivers and before we thaw user space. However, this argues not for doing the switch simply in the storage driver but to switch in the core. Regards Oliver -- 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
