linux-kernel - Re: [PATCH] HID: input: Add support for USI style events

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Message-ID: <YzcyUgLbZ2pVJSMO@google.com>
Date:   Fri, 30 Sep 2022 11:15:46 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Tero Kristo <tero.kristo@...ux.intel.com>,
        linux-input@...r.kernel.org, benjamin.tissoires@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: input: Add support for USI style events

On Fri, Sep 30, 2022 at 11:09:12AM +0200, Jiri Kosina wrote:
> On Thu, 25 Aug 2022, Jiri Kosina wrote:
> 
> > > Add support for Universal Stylus Interface (USI) style events to the HID
> > > input layers. The events are mapped as follows:
> > > 
> > > type	id	event
> > > ----	--	-----
> > > MSC(4)	6	Pen ID
> > > MSC(4)	7	Pen Color
> > > MSC(4)	8	Pen Line Style Ink
> > > MSC(4)	9	Pen Line Style Pencil
> > > MSC(4)	0xa	Pen Line Style Highlighter
> > > MSC(4)	0xb	Pen Line Style Chisel Marker
> > > MSC(4)	0xc	Pen Line Style Brush
> > > MSC(4)	0xd	Pen No Preferred Line Style
> > > ABS(3)	0x1c	Pen Line Width
> > > 
> > > All the listed MSC events are new, the ABS one is mapped to an existing
> > > event.
> > 
> > Dmitry, could you please Ack the MSC_PEN_* additions?
> 
> Dmitry, friendly ping on this one.

Very sorry, I meant to answer and forgot...

We need good descriptions of what exactly these events are, and when and
how userspace should expect/use them.

In general, I am wary of MISC_* namespace as it needs to be sent in
every packet as we do not retain state and do not give userspace way of
querying it, unlike ABS_* or KEY_* or number of other events.

Also, what do we do with multiple pens used at once? Maybe we do not
have such devices now, but multitouch devices did not exist in the
beginning either, and now are ubiquitous.

Thanks.

-- 
Dmitry