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SubjectRe: [PATCH] Input: reserve 2 events code because of HID
On Fri, Sep 07, 2018 at 10:51:15AM +0200, Benjamin Tissoires wrote:
> From: Benjamin Tissoires <benjamin.tissoires@redhat.com>
>
> 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_MISC+1 was never assigned a code, and so libinput
> can detect fake multitouch devices from genuine ones by checking is
> ABS_MISC+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+1 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@redhat.com>
> ---
>
> Hi,
>
> while reviewing my local tree, I realize that we might want to be able
> to differentiate older kernels from new ones that export REL_WHEEL_HI_RES.
>
> I know Dmitry was against adding several REL_MISC, so I hope just moving
> REL_WHEEL_HI_RES by one and reserving the faulty event codes would be good
> this time.
>
> This patch applies on top of the branch for-4.20/logitech-highres from
> Jiri's tree. It should go through Jiri's tree as well.

Hm, this is a bit ugly, bit I guess we could spare an event code.

Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

>
> Cheers,
> Benjamin
>
> include/uapi/linux/input-event-codes.h | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
> index 29fb891ea337..30149939249a 100644
> --- a/include/uapi/linux/input-event-codes.h
> +++ b/include/uapi/linux/input-event-codes.h
> @@ -708,7 +708,12 @@
> #define REL_DIAL 0x07
> #define REL_WHEEL 0x08
> #define REL_MISC 0x09
> -#define REL_WHEEL_HI_RES 0x0a
> +/*
> + * 0x0a is reserved and should not be used.
> + * It was used by HID as REL_MISC+1 and usersapce needs to detect if
> + * the next REL_* event is correct or is just REL_MISC + n.
> + */
> +#define REL_WHEEL_HI_RES 0x0b
> #define REL_MAX 0x0f
> #define REL_CNT (REL_MAX+1)
>
> @@ -745,6 +750,12 @@
>
> #define ABS_MISC 0x28
>
> +/*
> + * 0x29 is reserved and should not be used.
> + * It was used by HID as ABS_MISC+1 and usersapce needs to detect if
> + * the next ABS_* event is correct or is just ABS_MISC + n.
> + */
> +
> #define ABS_MT_SLOT 0x2f /* MT slot being modified */
> #define ABS_MT_TOUCH_MAJOR 0x30 /* Major axis of touching ellipse */
> #define ABS_MT_TOUCH_MINOR 0x31 /* Minor axis (omit if circular) */
> --
> 2.14.3
>

--
Dmitry

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