linux-kernel - Re: [PATCH 2/3] HID: hid-multitouch: support arrays for the split of the touches in a report

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Message-ID: <20120620165356.GA2850@polaris.bitmath.org>
Date:	Wed, 20 Jun 2012 18:53:56 +0200
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	"benjamin.tissoires" <benjamin.tissoires@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] HID: hid-multitouch: support arrays for the split of
 the touches in a report

Hi Benjamin,

> Win8 certification introduced the ability to transmit two X and two Y per
> touch. The specification precises that it must be in an array, with a
> report count == 2.
> 
> This test guarantees that we split the touches on the last element
> in this array.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...c.fr>
> ---
>  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 9a3891e..a5ef877 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -601,7 +601,10 @@ static int mt_event(struct hid_device *hid, struct hid_field *field,
>  			return 0;
>  		}
>  
> -		if (usage->hid == td->last_slot_field)
> +		if (usage->hid == td->last_slot_field &&
> +			usage == &field->usage[field->maxusage - 1])
> +			/* we only take into account the last report
> +			 * of a field if report_count > 1 */

This just looks so fragile... The report index should really be amount
the arguments to mt_event(). Since we rely on the pointer to reveal
the index, why not try something like (usage - &field->usage[0]) ==
(field->report_count - 1)? At least it shows clearly what we use the
point for.

>  			mt_complete_slot(td);
>  
>  		if (field->index == td->last_field_index
> -- 
> 1.7.10.2
> 

Thanks,
Henrik
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