On Tue, 24 Nov 2009, Sarah Sharp wrote:
> > There are several places where usbcore searches for altsetting 0. Can
> > they all use a single subroutine?
>
> Are you talking about lines like this?
>
> /* Dig the endpoints for alt setting 0 out of the
> * interface cache for this interface
> */
> intf_cache = new_config->intf_cache[i];
> for (j = 0; j < intf_cache->num_altsetting; j++) {
> if (intf_cache->altsetting[j].desc.bAlternateSetting == 0)
> alt = &intf_cache->altsetting[j];
> }
> if (!alt) {
> printk(KERN_DEBUG "Did not find alt setting 0 for intf %d\n", i);
> continue;
> }
>
> Sure, I can put that into a subroutine.
Good.
> On a similar note, what if the device doesn't have an alternate interface
> setting 0? What should usb_hcd_alloc_bandwidth() do when installing a new
> configuration with an interface that doesn't have an alt setting 0? What
> alternate interface setting will the device think it's at after it receives the
> set configuration command?
>
> I see that usb_reset_configuration() has this note:
>
> /* No altsetting 0? We'll assume the first altsetting.
> * We could use a GetInterface call, but if a device is
> * so non-compliant that it doesn't have altsetting 0
> * then I wouldn't trust its reply anyway.
> */
> if (!alt)
> alt = &intf->altsetting[0];
Yes; there's a similar note in usb_set_configuration().
> If I follow that example, usb_hcd_alloc_bandwidth() should pick the first alt
> setting if there is no alt setting 0 for a new configuration. That means I
> need to set intf->cur_altsetting to that alt setting before
> usb_reset_and_verify_device() calls usb_set_interface().
Correct. It's not likely to come up in practice -- I've never heard of
a device with no altsetting 0.
Alan Stern
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