On Thu, Feb 24, 2005 at 10:30:17AM -0500, Alan Stern wrote: > Anyway there's no reason to put the extra information about inactive > configurations or altsettings in sysfs, since it's already available in > usbfs.
> Your program can always use the information in /proc/bus/usb/devices, or > it can read the descriptors directly from the device's file in usbfs. It > could even parse the output from lsusb. It's very clean to pull data out of sysfs, since everything is nice and cleanly cross-linked (with symlinks); to connect to the usbfs device file, I need to find it (given a sysfs path). The data in usbfs and lsusb isn't broken out: sysfs splits each piece of data into a separate file, so it can all be accessed without substantial parsing, which is inherently more reliable. Also, reading /proc/bus/usb/devices or lsusb -v will (currently) query string descriptors, even if I don't want them at all (and usb/devices will do so for all devices, not just the ones I'm interested in). I suppose that the cross-referencing problems could be fixed, at least, by having a file with the relative usbfs path of the device: "usbfs" = "001/002". (The information still wouldn't be as easily available, though.) > It's probably not a good idea to prefer the lower-power configuration by > default. A better heuristic might be to prefer the highest-power > configuration that fits within the parent hub's power budget. A quick look suggests that doing this against the 100mA per-port cap should be fairly easy, but I don't know how to do this for the power limit of the whole hub: when the first device is inserted, it needs to choose a low-enough power config that we have enough for the second card that's not inserted yet (and, presumably, without having to second-guess and change the configuration later). Since the power limit of the whole hub appears to also be 100mA, that seems to be--for this particular case--"prefer the highest-power configuration <= 50mA" (100mA over 2 devices). Is there a better approach? -- Glenn Maynard ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
