> * Zero is not a valid configuration value as it is used to reference the
> unconfigured state.
So requesting a device to assume that configuration violates the
specification ?
> * Other than that the only requirement for the configuration value(s) is
> they must be unique for the device. In conclusion, there's nothing wrong
> with a device using configuration values 13, 7, 123 for its three
> configurations - in any order.
>
> * configuration values are known in advance (i.e. before the host needs to
> issue the first SetConfiguration request) from the corresponding
> configuration descriptor.
>
> * configuration descriptors (like all other deescriptors) are referenced
> by a zero-based index 0, 1, ... bNumConfigurations-1 where the number of
> configurations is known from the device descriptor (bNumConfigurations)
> To repeat: These indices refer to the configuration descriptors, not the
> configuration.
But there's 1:1 correspondence between configuration descriptors
and valid configurations, isn't there?
> * A priori there is nothing that makes any configuration different or
> preferable compared to any other. The choice is just a matter of user
> selection, policies and system configuration.
True, but absent user intervention the kernel has to choose a
configuration. We'd like to call that the default configuration.
The patches I've sent in aim to make selecting a configuration
through usbfs safe. The possibility itself has been there for a long time.
Additional questions, may a hub have several configurations ?
May changing a hub's configuration lead to its children being
disconnected ? Must the hub single disconnections to the host
before it changes its configuration, if that leads to child
disconnection ?
TIA
Oliver
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