Hi On Sat, Dec 14, 2013 at 8:14 AM, Reyad Attiyat <reyad.attiyat@xxxxxxxxx> wrote: > I have a basic question about the way the linux kernel handles human > input devices. I bought a Surface Pro 2 with a Type cover keyboard. > This did not work out of the box with stock linux kernel 3.11. When I > added the hardware id of the device to the hid-microsoft.c driver it > worked. > > Does this work simply because when I add the hardware id to the > driver, the kernel knows to use usb-hid generic driver with the > device? I'm trying to understand the hid-microsoft driver and it seems > to apply quirks/hacks that enable Microsoft devices to work with the > hid driver. Such as remapping keys. I don't need any of these quirks > as all the media keys on the keyboard work all by adding the hardware > id. > > Why doesn't the device work out of the box? Is the device not > advertising itself as a hid device over usb? I'm little confused as to > how this should be fixed. Does the kernel fail in noticing this hid > device or does the device fail in telling the kernel it is a > keyboard/mouse? There are lots of HID devices out there that either don't follow the HID specification or are not covered by the specification. Such devices cannot be supported out-of-the-box. How should we know how they work? That's why we provide lots of HID quirks for such devices. The hid-microsoft driver is one of them. It applies a bunch of fixups so HID core knows how it works. We could use some broader heuristics to detect such devices, however, the conservative approach is the safest. That means, only device-IDs that have been reported to work are added to the hid-quirk lists. This way, we don't break well-defined working devices via false positives, but on the other hand, every new device needs to be added manually. If you have suggestions how to improve this situation, please provide patches. But input-development (or generally kernel development) must be conservative in that regard. A regression is never acceptable and we'll revert such patches. So someone has yet to come up with better heuristics or we'll keep our ID lists. Cheers David -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
