Re: RFC: Platform data for onboard USB assets

Mark Brown
2011-03-11T17:08:11Z

On Fri, Mar 11, 2011 at 08:56:42AM -0800, Greg KH wrote:
> On Fri, Mar 11, 2011 at 04:48:50PM +0000, Mark Brown wrote:

> > USB itself is discoverable but the when the USB bus you're looking at is
> > one that's soldered down onto a board in a specific design all bets are
> > off regarding how complete the information you get will be. On a basic
> > level the designers may have done things like omit the configuration
> > EEPROMs that would set the device IDs that the driver should be relying
> > on to identify the hardware configuration. There may be other, nastier,
> > things going on.

> Then you use the existing platform data for your USB host controller
> driver. Doesn't that work today just fine?

Wrong end of the bus. This stuff is simple enough to deal with in a
system specific fashion, the standard solution would be to patch the
relevant drivers to hard code whatever is required.

> > You really can't make this assumption about discoverable buses on
> > embedded devices. The discoverability will get you most of the way
> > there but not always all of the way there.

> Then the bus is not really USB, sorry. USB is discoverable, _and_ can
> support enumeration in non-deterministic ways. If people are using it
> in other ways then it is not USB and is something else.

That's certainly a valid way of looking at things but it doesn't really
move mainline support for systems which do stuff like this forward.

On the bright side I don't generally have to work on this stuff myself :)