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List:       linux-input
Subject:    Re: HID Output and Feature Reports
From:       Joao Paulo Rechi Vita <jprvita () openbossa ! org>
Date:       2012-05-29 22:14:47
Message-ID: CAAngNMa1EZN-U5MZ6kwMJbUs0F2v-3A3UyaSz8+v1Uy6+BMLrg () mail ! gmail ! com
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Hello David,

On Sat, May 26, 2012 at 7:44 AM, David Herrmann
<dh.herrmann@googlemail.com> wrote:
> Hi Joao
>
> I CC'ed Jiri as he is the HID maintainer.
>
> On Fri, May 25, 2012 at 10:51 PM, Joao Paulo Rechi Vita
> <jprvita@openbossa.org> wrote:
>> Hello all,
>>
>> I'm working to support HID over GATT (HoG), which is HID over
>> Bluetooth Low Energy links, both on kernel and userspace. Traffic
>> coming from the remote peripheral through a L2CAP socket will be
>> handled in usespace, where the HID input reports are decapsulated from
>> GATT and injected back into the kernel through the new uHID module
>> written by David Herrmann. This module works similar to uinput, but
>> dealing with HID traffic.
>>
>> The input part is working without problems and now I looking how to
>> support Output and Feature reports. Doing some basic testing it seems
>> we don't support Output reports very well. A basic use-case for that
>> is synchronizing keyboard leds (CAPS, NUM, etc) when there is more
>> than one keyboard connected, and I couldn't get this to work on my
>> tests. I didn't try to test feature reports since it's still not very
>> clear to me when they're used. The HID spec says that they exist for
>> setting values/controls on the peripheral that are not visible to the
>> user, but I haven't discovered any real-world use case for them. What
>> is the current state for these reports, do we support them somehow?
>
> I think my last revision of uhid added support for feature-reports.
> However, they are not used by the generic hid-input driver. If there
> is currently no specialized bluetooth-LE HID driver, you also do not
> need to worry about it.
>

Yes, I've seen the new event types for them, what I'm looking for is
how to trigger them.

> I think the new generic HID battery-detection code uses the
> feature-reports. However, its disabled by default if I remember
> correctly.
>

I will check this out, thanks for the hint.

> About output-reports: Do you correctly receive the UHID_OUTPUT_EV
> request in user-space? Do you send the packet to the device? How do
> you format it?
>

I was correctly receiving it with the previous version of your patch.
With this new version I still receive an event coming from the host,
but with ev.type value out of the enum range (different values like
this: 2062073856).

What is the difference between UHID_OUTPUT_EV and UHID_OUTPUT events?
Should both of them be written to the device?

>> Also, I've found usbhid-dump by Greg K-H, but it doesn't seem to dump
>> data coming from the host to the device. Is this on the plans for this
>> tool? I can try to send a patch for it, if someone can guide me on how
>> this whole output/feature reports thing should work.
>
> Regards
> David

-- 
João Paulo Rechi Vita
Openbossa Labs - INdT
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