linux-kernel - Re: [PATCH] hid: add two led codes to hid input mapping

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Date:	Mon, 2 Apr 2007 09:06:07 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Dan Engel" <dan@...rceharvest.com>
Cc:	"Jiri Kosina" <jkosina@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hid: add two led codes to hid input mapping

On 4/2/07, Dan Engel <dan@...rceharvest.com> wrote:
> On Mon, 2007-04-02 at 00:04 -0400, Dmitry Torokhov wrote:
>
> > Actually I want to keep input subystm out of the loop here, since LEDs
> > such as mail, charging, etc have nothing to do with user input but
> > rather reflect overall system/application state.
> >
>
> What if I just added a HID_QUIRK_HIDDEV for the vendor/product id's in
> the blacklist table in hiddev.c. That would force the creation of a
> hiddev device, through which a user-space program could access the HID
> usages directly.
>
> It would be awkward, though, since there would also be an input event
> device, but one through which the full functionality is not accessible.

What other evets/usages does this device support?

> Is there a HID_QUIRK that would force creation of a hiddev *instead of*
> (rather than in addition to) an event dev?

No but it could be added.

>
> Two things to keep in mind:
>
> 1) The device in question (it's a Belkin USB Flip KVM switch, just to
> restate from the OP) has nothing to do with LED's. It just overloads the
> LED HID usage codes to receive control from the PC.

Ah, OK.

> 2) No matter what we do in terms of presenting this device to user-land,
> under the hood it's a HID-class USB device, and it probably doesn't make
> sense to not make use of that.

It may be a HID-class device but it is definetly not an input device
and it would be wrong to present it to userspace as a device having 2
LEDs on it - it would be a lie. If we did that then some application
might mistake the device for something else and decide to switch that
LED off thus turning your KVM off. A random application should not be
aware how a random vendor decided to interpret the specs.

-- 
Dmitry
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