linux-kernel - Re: [PATCH v4] HID: hid-multitouch: support fine-grain orientation reporting

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Message-ID: <20171011135324.GI865@mail.corp.redhat.com>
Date:   Wed, 11 Oct 2017 15:53:24 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Dmitry Torokhov <dtor@...omium.org>,
        Henrik Rydberg <rydberg@...math.org>,
        Wei-Ning Huang <wnhuang@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Input <linux-input@...r.kernel.org>,
        Peter Hutterer <peter.hutterer@...-t.net>
Subject: Re: [PATCH v4] HID: hid-multitouch: support fine-grain orientation
 reporting

On Oct 11 2017 or thereabouts, Jiri Kosina wrote:
> On Wed, 11 Oct 2017, Benjamin Tissoires wrote:
> 
> > I am not sure if libinput even uses ABS_MT_ORIENTATION
> 
> I don't think it does, so that should be okay. However ...

I had a meeting this Peter at noon today. The summary is that libinput
doesn't uses ABS_MT_ORIENTATION, and that the documentation requires
actually 3 things:
- 0 is Y-aligned, up ("north")
- maximum should be aligned with X, pointing toward the right ("east")
- negative and out of range values are allowed

>From this, we can conclude that the minimum doesn't matter, as long as
it is 0 or -max, it is the same from the user space point of view.

One thing that the documentation suggests is that if we report [0, max],
this would indicate that out of ranges values won't be triggered, and
[-max, max] would seem to indicate that the data might be negative and
so out of range values would be acceptable.

Anyway, no changes in any cases from userspace.

> 
> > , but I'd go for fixing the documentation. And re-reading it, it's not 
> > clear that the doc tells us to have [0,90]. It mentions negative values 
> > and out of ranges too, so we might just as well simply clarify that we 
> > rather have [-90,90], with 0 being "north".
> 
> ... I'd like the documentation fix to go in together in one go with this 
> patch if possible.
> 

Sounds like a plan.

Cheers,
Benjamin

> Thanks,
> 
> -- 
> Jiri Kosina
> SUSE Labs
>