On Wed, 21 Jul 2010 23:44:25 +0200, Adam Kropelin <akropel1@xxxxxxxxxxxxxxxx> wrote:
I have a composite device which consists of an RNDIS interface as well
as several additional standard interfaces (cdc-serial, umass, etc.).
These are all contained in a single configuration using IADs. I've
discovered that kernels without CONFIG_USB_NET_RNDIS_HOST enabled will
refuse to select any configuration, rendering the standard interfaces
inaccessible (at least without additional jiggering). I traced this
back to generic.c:usb_choose_configuration() which rejects
configurations whose first interface is RNDIS when RNDIS is not
enabled:
| if (i == 0 && desc && (is_rndis(desc) || is_activesync(desc))) {
|#if !defined(CONFIG_USB_NET_RNDIS_HOST) && !defined(CONFIG_USB_NET_RNDIS_HOST_MODULE)
| continue;
|#else
| best = c;
|#endif
| }
I would propose one of two solutions: (A) Reject the configuration as
we do today, but only if there are additional configurations available
to choose from (i.e. bNumConfigurations > 1), or (B) Reject the
configuration only if there are no additional interfaces in the config
besides RNDIS.
I lean toward (A).
In the broader case, to some extent I wonder if the logic in
usb_choose_configuration() should be as simple as choosing the one and
only config regardless of any heuristics in all cases where only a
single config is present. Is there value in failing to select any
configuration at all?
I had an idea once to make the code choose configuration with the smallest
bConfigurationValue. This way, composite devices could provide RNDIS
configuration as the first one with bConifgurationValue == 2 and the other
configuration, as second one, with bConfigurationValue == 1. This is what
Ethernet gadget does for instance.
Windows would still choose the first configuration so all would be grand.
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