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SubjectRe: [PATCHv3 2/4] usb: gadget: replace "is_dualspeed" with "max_speed"
On Wed, Aug 24, 2011 at 10:31:27AM -0400, Alan Stern wrote:
> On Wed, 24 Aug 2011, Michal Nazarewicz wrote:
>
> > On Tue, 23 Aug 2011 22:49:37 +0200, Alan Stern <stern@rowland.harvard.edu>
> > wrote:
> > > Still, maybe I was wrong. Maybe it would be better to use the fastest
> > > speed supported by at least one of the function drivers. The user can
> > > always force a SuperSpeed-capable device to run at high speed by using
> > > a USB-2 cable to plug it in. I'm not sure whether the user could force
> > > such a device to run at full speed, however.
> >
> > I'm actually wondering whether we really need to worry about it.
> > composite_driver has the “max_speed” field and I would just leave it as
> > composite driver's author responsibility to put correct value there.
> >
> > One thing that could be worth doing is iterate over all the configurations
> > and figure out if at least one supports the speed declared by “max_speed”
> > and if not, lower it.
>
> That's the same as what I said: Use the highest speed supported by any
> function driver. There really isn't any point in allowing connections
> faster than that. And as Felipe pointed out, the user always has the
> capability to force the connection to be slower, by using the right
> sorts of cables and hubs.
>
> > Like I've said before, as additional functionality, composite.c could
> > check if it's USB_SPEED_UNKWONW in which case it would look for the lowest
> > speed that all the functions support.
> >
> > Such configuration would allow composite driver authors set the speed to
> > USB_SPEED_SUPER when they mean “choose maximum speed at least one function
> > supports” and to “USB_SPEED_UNKWONW” when they mean “choose maximum speed
> > all the functions support”.
> >
> > Does that make sense?
>
> It's reasonable. Just be sure to document it properly; otherwise
> nobody will understand or remember it!

good point. I agree with this approach.

--
balbi
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