Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> writes: > On Mon, Mar 11, 2013 at 10:00:21PM +0100, Bjørn Mork wrote: >> Userspace applications need to know the maximum supported message >> size. > > Can't they get that from sysfs from the USB field that defines this? Not at the moment since we don't export it. But that is of course easy to fix. This was how I started. The next problem was that this "message size" property is common to all drivers using the cdc-wdm code (cdc-wdm, cdc_mbim and qmi_wwan), and they all have different USB descriptors defining it. So you would have 3 different fields (if you decided to add a pseudo field for qmi_wwan, which hard codes a sane value) for the same property. This made me create the first patch, which added a common sysfs propery to the cdc-wdm device instead. The response to that was "I would say that the most generic solution would be an ioctl()" > Adding a new ioctl is usually not a good idea, who is going to change > the userspace tools to properly call this ioctl? That will be Aleksander's job :) No, being serious I do realize the problem and I don't know if it is such a good idea either. But I do know that we need some way for the driver to let userspace know this value without having to guess too much. Currently, when a userspace application sees a /dev/cdc-wdmX device, it will have to - check which USB interface it belongs to, - parse the DMM descriptor if it is CDC WDM, - parse the MBIM descriptor if it is CDC MBIM - check if the driver is qmi_wwan if none of the above - know which value qmi_wwan has hard coded No application does this. Bjørn -- 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
