Messages in this thread | | | Date | Fri, 11 Mar 2011 14:12:10 -0500 (EST) | From | Alan Stern <> | Subject | Re: RFC: Platform data for onboard USB assets |
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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
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