linux-kernel - Re: [PATCH v2] Input: reserve 2 events code because of HID

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Date:   Thu, 4 Oct 2018 21:09:43 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Harry Cutts <hcutts@...omium.org>,
        Peter Hutterer <peter.hutterer@...-t.net>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Input: reserve 2 events code because of HID

On Thu, 4 Oct 2018, Benjamin Tissoires wrote:

> Prior to commit 190d7f02ce8e ("HID: input: do not increment usages when
> a duplicate is found") from the v4.18 kernel, HID used to shift the
> event codes if a duplicate usage was found. This ended up in a situation
> where a device would export a ton of ABS_MISC+n event codes, or a ton
> of REL_MISC+n event codes.
> 
> This is now fixed, however userspace needs to detect those situation.
> Fortunately, ABS_MT_SLOT-1 (ABS_MISC+6) was never assigned a code, and
> so libinput can detect fake multitouch devices from genuine ones by
> checking if ABS_MT_SLOT-1 is set.
> 
> Now that we have REL_WHEEL_HI_RES, libinput won't be able to differentiate
> true high res mice from some other device in a pre-v4.18 kernel.
> 
> Set in stone that the ABS_MISC+6 and REL_MISC+1 are reserved and should not
> be used so userspace can properly work around those old kernels.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
> 
> Dmitry, I did not take your Acked-by, as I added 2 new events and wanted to
> be sure you are still OK.
> 
> Jiri, this will still need to go through your tree, as the input-event-codes
> changes that introduce REL_WHEEL_HI_RES are in your for-4.20/logitech-highres.

Applied, thanks Benjamin.

-- 
Jiri Kosina
SUSE Labs