On Thu, Aug 16, 2012 at 09:58:14AM +0200, Sebastian Andrzej Siewior wrote: > * Felipe Balbi | 2012-08-16 09:30:05 [+0300]: > > >I couldn't find anywhere in the USB Specification > >where it requires us to make sure all interfaces start > >on Alternate Setting zero. IMHO, we should consider > >initial state as UNKNOWN and not rely on that being > >zero or anything. > > Table 9-1 in USB2.0 spec says once a device is configured (after > USB_REQ_SET_CONFIGURATION) is may use its functions. So the default > function should be activated. > > 9.6.5 says: > |An interface may include alternate settings that allow the endpoints > |and/or their characteristics to be varied after the device has been > |configured. The default setting for an interface is always alternate > |setting zero. > |The SetInterface() request is used to select an alternate setting or to > |return to the default setting. > > That means we have to start at zero. The host may change it, it may not > use SetInterface() at all if the default setting is fine. > > 9.1.1.5 says: > |Configuring a device or changing an alternate setting causes all of the status > |and configuration values associated with endpoints in the affected > |interfaces to be set to their default values. > > I think we can skip ->set_alt() if the old setting is the same as the > new one. Good finding, then the current state is correct and functions should handle any transients that this can cause ;-) -- balbi
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