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    SubjectRe: [linux-usb-devel] [RFC] HID bus design overview.
    On Thursday 29 March 2007 23:06, Li Yu wrote:
    > Dmitry Torokhov wrote:
    > > On 3/28/07, Jiri Kosina <> wrote:
    > >>
    > >> The crucial thing here is that all reports but the ones that the driver
    > >> registered to will be processed in a standard way by the generic hid bus
    > >> layer, and those reports that the driver registered to will be
    > >> ignored by
    > >> the layer, and passed for processing to the driver.
    > >>
    > >
    > > I don't think it is a good idea to register driver for specific
    > > usages/reports. Quite often you want to adjust processing of a report
    > > for a specific device. What if there are 2 devices that need such
    > > quirks? How will you do hotplug and module loading? Emit new uevent
    > > for every report? Also, what about users and Kconfig? "Driver for
    > > usage 0x000012345. Say Y if your hardware does not wotk correctly with
    > > defautl handler for this usage and require special processing"???
    > >
    > > Just register based on VID/PID and provide standard
    > > hid_default_input_event() to drivers so they would call it for reports
    > > they don't need to do special processing on.
    > >
    > I think the shadow driver can not share inputdev with the related
    > fundamental driver, so here are two input devices for one hid_device,
    > how we should process both? It seem we have three choices:
    > 1. Shadow | Fundamental means
    > I think this is Jiri said. Fundamental driver handle all common
    > input events, and Shadow driver handle anther specific input events,
    > this imply user space process need monitor both input devices at same
    > time, I do not think this is good idea.
    > 2. Shadow & Fundamental means
    > Let Fundamental driver and Shadow driver work at same time! but
    > shadow also handle specific input event. So, the user may get twice
    > input events! For example, the keyboard input in console.
    > Also, I do not like this.
    > 3. Shadow ^ Fundamental means
    > Let Shadow driver handle every thing, and fundamental device silent,
    > even unregister it. I think this is best choice between them, this means
    > have a bit of complex.

    There should be one device and your driver should simply do:

    static void my_driver_hid_event(struct hid_device *hid, struct hid_field *field,
    struct hid_usage *usage, __s32 value)
    if (special_processing_needed(usage)) {
    input_event(field->hidinput->input, XXX, YYY, ZZZ);

    } else
    hidinput_hid_event(hid, field, usage, value);

    That is pretty much it. Your driver is not a shadow driver, it is
    regular driver on HID bus that just happens to use generic hander
    for standard events.

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