On Tue, Aug 3, 2010 at 10:27 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 3 Aug 2010, Xiaofan Chen wrote: > >> On Mon, Aug 2, 2010 at 6:22 PM, Felipe Balbi >> <felipebalbi@xxxxxxxxxxxxxxxxxxxxx> wrote: >> >> Another one is that libusb caches the descriptors, so subsequent >> >> get descriptor requests will just return the cached version, but USBCV >> >> that's a no-no since we need to exercise a real GetDescriptor() request. >> >> I understand why libusb does that (to avoid waking up a sleeping device), >> >> but would there be a way to overcome that ? >> >> >> >> I like this idea. I believe it is necessary to wake up the device >> sometimes. Maybe a flag (refresh or similar) can be added to the >> libusb-1.0 APIs related to the descriptor so that a "fresh" copy of the >> descriptors can be read from the device. >> http://libusb.sourceforge.net/api-1.0/group__desc.html > > USBCV is such a specialized application that I wouldn't recommend > changing libusb just to accomodate it. Besides, you can always send > the Get-Descriptor request yourself, as a normal control transfer, > rather than relying on libusb_get_descriptor. > I see. Thanks for the explanation. The reason I would like to use a refresh is to wake up the device without opening it again. >Under Linux, a suspended device will be woken up as soon as > libusb opens the device file. Then why libusb caches the descriptors if avoiding to wake up a sleeping device is the goal? -- Xiaofan -- 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
