Re: RFC: Platform data for onboard USB assets

Alan Stern
2011-03-11T19:12:14Z

On Fri, 11 Mar 2011, Andy Green wrote:

> I don't believe I referred to class devices anywhere. It does not
> matter if the main chip function is class device or not.

It matters because the class specification for a USB device is never
going to mention information sources that are outside the USB protocol,
such as board definitions. Consequently a class driver will never need
to use such a thing.

> If there is any kind of "functional implementation" knowledge that is
> outside the chip and driver itself, it has to be held somewhere, and
> applied appropriately. platform_data from the board definition file is
> the established place for that knowledge that is specific to a board.

Since essentially all of the USB drivers currently in the kernel _are_
class drivers (at least, I'm not aware of any non-trivial exceptions),
this means none of the existing USB drivers should need to access any
platform data.

Of course, this doesn't rule out the possibility of platform-specific
USB drivers that _do_ need this information.

> > Also, do you have a real example of a USB driver today that needs this?
>
> I think you find without devpath -> platform_data mapping, the kind of
> layout given above is made quite difficult to support in Linux.

What would be needed to support such a mapping? It seems to me that we
probably have all the necessary ingredients in place already.

Alan Stern