Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET_SUPERSPEED

[Yang Rui Rui]

On 08/19/2011 01:05 AM, Michal Nazarewicz wrote:
> On Thu, 18 Aug 2011 16:59:28 +0200, Alan Stern<stern@xxxxxxxxxxxxxxxxxxx>
> wrote:
>
> > 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.
>
> Yeah, that's why you set usb_gadget_driver's speed to the speed declared
> in usb_composite_driver.

This is what I means in before reply, musb_gadget_start will check the speed set here.
if it != USB_SPEED_HIGH it will return -EINVAL.

> For the most part, usb_composite_probe() is called only once in module's
> init function.  As far as I know, only g_ffs calls it several times.  So
> in all cases expect for g_ffs, composite_driver.speed =
> min(composite_driver.speed,
> driver->max_speed) should have the same effect as composite_driver.speed
> = driver->max_speed.

For original code, ifndef CONFIG_USB_GADGET_SUPERSPEED and max_speed = USB_SPEED_SUPER
then the result will be:

composite_driver.speed = min(USB_SPEED_HIGH, USB_SPEED_SUPER)

For patched code, composite_driver.speed = USB_SPEED_SUPER

> > 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.
>
> Shouldn't that be dealt in usb_add_function()?  I cannot see any code that
> would do that here atm though.


--
Thanks
Yang Ruirui
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