linux-kernel - Re: [PATCH v5 4/10] HID: multitouch: support getting the contact ID from HID_DG_TRANSDUCER

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Message-ID: <xdkn2y6wpnqjrngem3xjxjn2a7cykhrb6dj56w6avz4noj7itu@xlknbwmp63h7>
Date: Fri, 27 Sep 2024 17:56:19 +0200
From: Benjamin Tissoires <bentiss@...nel.org>
To: Aditya Garg <gargaditya08@...e.com>
Cc: "tzimmermann@...e.de" <tzimmermann@...e.de>, 
	"maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>, "mripard@...nel.org" <mripard@...nel.org>, 
	"airlied@...il.com" <airlied@...il.com>, "daniel@...ll.ch" <daniel@...ll.ch>, 
	Jiri Kosina <jikos@...nel.org>, Thomas Weißschuh <thomas@...ch.de>, 
	Orlando Chamberlain <orlandoch.dev@...il.com>, Kerem Karabay <kekrby@...il.com>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v5 4/10] HID: multitouch: support getting the contact ID
 from HID_DG_TRANSDUCER_INDEX fields

On Aug 17 2024, Aditya Garg wrote:
> From: Kerem Karabay <kekrby@...il.com>
> 
> This is needed to support Apple Touch Bars, where the contact ID is
> contained in fields with the HID_DG_TRANSDUCER_INDEX usage.
> 
> Signed-off-by: Kerem Karabay <kekrby@...il.com>
> Signed-off-by: Aditya Garg <gargaditya08@...e.com>
> ---
>  drivers/hid/hid-multitouch.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index 56fc78841..3e92789ed 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -635,7 +635,9 @@ static struct mt_report_data *mt_allocate_report_data(struct mt_device *td,
>  
>  		if (field->logical == HID_DG_FINGER || td->hdev->group != HID_GROUP_MULTITOUCH_WIN_8) {
>  			for (n = 0; n < field->report_count; n++) {
> -				if (field->usage[n].hid == HID_DG_CONTACTID) {
> +				unsigned int hid = field->usage[n].hid;
> +
> +				if (hid == HID_DG_CONTACTID || hid == HID_DG_TRANSDUCER_INDEX) {

I'm not super happy about this. The HID spec specifically mentions
CONTACTID to be related to multitouch, when TRANSDUCER is not
specifically for multitouch. I would rather have this hidden behind a
quirk, because I don't think this is standard (the device comes from an
environment where both the hardware and the software stack is
controlled, which already gave some fun decisions from Apple).

Cheers,
Benjamin

>  					rdata->is_mt_collection = true;
>  					break;
>  				}
> @@ -814,6 +816,7 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
>  			MT_STORE_FIELD(tip_state);
>  			return 1;
>  		case HID_DG_CONTACTID:
> +		case HID_DG_TRANSDUCER_INDEX:
>  			MT_STORE_FIELD(contactid);
>  			app->touches_by_report++;
>  			return 1;
> -- 
> 2.43.0
>