linux-kernel - Re: [PATCH 1/3] Input: mt - prevent balanced slot assignment to assign twice the slot

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Message-ID: <20150331145818.GA30670@mail.corp.redhat.com>
Date:	Tue, 31 Mar 2015 10:58:19 -0400
From:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:	Henrik Rydberg <rydberg@...math.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Peter Hutterer <peter.hutterer@...hat.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Input: mt - prevent balanced slot assignment to
 assign twice the slot

Hi Henrik,

On Mar 31 2015 or thereabouts, Henrik Rydberg wrote:
> Hi Benjamin,
> 
> > If two touches are under the dmax distance, it looks like they can now
> > be assigned to the same slot. Add a band aid to prevent such situation
> > and be able to use the balanced slot assignment.
> 
> Yes, great find. You patch is correct, but it is not a band aid, but a
> result stemming from a limitation in how equality constraints (read
> unique assignments) can be handled in the iterative algorithm. This
> cannot happen in the original algorithm, because of the extra
> penalization for overcovers.
> 
> Here is an alternative version which cleans up the loop logic
> somewhat, together with a different commit message. I did not have any
> opportunity to check this in hardware. I you like it and find it
> working, then please take over the authorship and just add a
> signed-off from me.

OK, it works just fine. So I'll resend the series with Hans' ACK and
your v2. Thanks for your quick respin.

Cheers,
Benjamin

> 
> Thanks,
> Henrik
> 
> ---
> 
> From e00d63f6cadf20d871bed763b3531428b34d785c Mon Sep 17 00:00:00 2001
> From: Henrik Rydberg <rydberg@...math.org>
> Date: Tue, 31 Mar 2015 09:10:02 +0200
> Subject: [PATCH] Input: MT - make slot assignment work for overcovered
>  solutions
> 
> The recent inclusion of a deassignment cost in the slot assignment
> algorithm did not properly account for the corner cases where the
> solutions are overcovered. This patch makes sure the resulting assignment
> is unique, allocating new slots when necessary.
> 
> UNTESTED
> ---
>  drivers/input/input-mt.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
> index fbe29fc..17e80a6 100644
> --- a/drivers/input/input-mt.c
> +++ b/drivers/input/input-mt.c
> @@ -363,25 +363,28 @@ static void input_mt_set_slots(struct input_mt *mt,
>  			       int *slots, int num_pos)
>  {
>  	struct input_mt_slot *s;
> -	int *w = mt->red, *p;
> +	int *w = mt->red, j;
>  
> -	for (p = slots; p != slots + num_pos; p++)
> -		*p = -1;
> +	for (j = 0; j != num_pos; j++)
> +		slots[j] = -1;
>  
>  	for (s = mt->slots; s != mt->slots + mt->num_slots; s++) {
>  		if (!input_mt_is_active(s))
>  			continue;
> -		for (p = slots; p != slots + num_pos; p++)
> -			if (*w++ < 0)
> -				*p = s - mt->slots;
> +		for (j = 0; j != num_pos; j++)
> +			if (w[j] < 0) {
> +				slots[j] = s - mt->slots;
> +				break;
> +			}
> +		w += num_pos;
>  	}
>  
>  	for (s = mt->slots; s != mt->slots + mt->num_slots; s++) {
>  		if (input_mt_is_active(s))
>  			continue;
> -		for (p = slots; p != slots + num_pos; p++)
> -			if (*p < 0) {
> -				*p = s - mt->slots;
> +		for (j = 0; j != num_pos; j++)
> +			if (slots[j] < 0) {
> +				slots[j] = s - mt->slots;
>  				break;
>  			}
>  	}
> -- 
> 2.3.0
> 
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