On Thu, 18 Aug 2011, Michal Nazarewicz wrote:
On Wed, 17 Aug 2011 23:09:37 +0200, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
wrote:
> I see what's going on here. Your original patch was wrong and then my
> correction was wrong as well.
>
> This line has to remain the way it was (although those (u8) typecasts
> don't seem to be necessary). Above, you have to initialize
> composite_driver.speed to an appropriate value, probably
> USB_SPEED_SUPER.
>
> What you didn't realize in your original patch is that
> usb_composite_probe() gets called more than once. Each time it is
> called, it has to adjust composite_driver.speed.
That's sneaky of composite.c... But is it desired behaviour?
Yes, it is.
I cannot
came up with a situation where that's what we want. I would imagine that
usb_composite_probe() should assume the same speed for given
usb_composite_driver regardless if some other slower usb_composite_driver
was loaded.
The speed being calculated isn't the speed of the usb_composite_driver;
it's the speed of the usb_gadget_driver. The gadget itself cannot be
allowed to run faster than its internal drivers can handle.
For example, if you have a composite gadget where one of the function
drivers can handle SuperSpeed and the other can't go beyond high speed,
the overall gadget must never run faster than high speed.