On Fri, Mar 11, 2011 at 04:51:53PM +0000, Andy Green wrote: > On 03/11/2011 04:45 PM, Somebody in the thread at some point said: > > Hi - > > >Or to put it another way... With external, hot-plugged USB devices, > >there is no need to know "how it is wired". The fact that it is on a > >USB bus is the only information necessary. Why does anyone need to > >know more than this for on-board USB devices? > > For example, the USB device is a chip with option pins. On the > board it is placed on, some of the option pins are tied in a > particular way that impacts its actual function, but can't be seen > from the chip itself. The driver covers all the options, but it > needs to be told which mode the chip was wired up for. Then that information is in the driver that was written for that specific device, it is NOT a class device if it requires this type of information to work properly. > Another example, it's a USB chip with GPIO pins, analogous to a I2C > GPIO extender. Some of the GPIO are wired to LEDs also on the > board, which you want to expose as generic GPIO. The board > definition file is in a position to do all that because it knows > what the board is and what it is wired up to. > > That the USB chips in these examples are 'discoverable' has nothing > to do with anything. In fact the board definition file has > knowledge about the "functional implemntation" of the instances of > those chips -- just exactly those instances soldered to the board. > If you plugged another of these chips, the board definition file has > nothing to say about it because they are not "on the board" and > in-scope for it. Then put that information in the specific driver for this type of device. Also, do you have a real example of a USB driver today that needs this? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
