Re: [PATCH] Input: MT - Add support for balanced slot assignment

[Benjamin Tissoires <benjamin.tissoires@gmail.com>]

On Feb 01 2015 or thereabouts, Henrik Rydberg wrote:
> Hi Benjamin,
> 
> > Tested this morning, and yes, it solves the problem.
> > I assumed that the dmax was in mm, and used "10 * priv->x_res", which
> > seemed to do the trick:
> > - tapping with two fingers side by side triggered the jumps
> > - in the general case (switching from the index to the thumb to
> > click), the jumps disappeared.
> 
> Great, thanks for testing.
> 
> > Maybe we should also add a doc telling which units the dmax should be.
> 
> I added an enhanced description, which hopefully clarifies the units
> of dmax.
> 
> > When you'll sign this, you can add my tested-by.
> 
> Done, and tested against Linus' master. I take it you have a patch on
> this coming up as well?

Yep. I have a one line patch to enable the feature in synaptics. I will
send it as soon as Dmitry take this one.

Cheers,
Benjamin

> 
> Thanks,
> Henrik
> 
> From 2a4986420e634df2f0ba09198cb1e55714f61577 Mon Sep 17 00:00:00 2001
> From: Henrik Rydberg <rydberg@bitmath.org>
> Date: Sun, 1 Feb 2015 09:16:10 +0100
> Subject: [PATCH v2] Input: MT - Add support for balanced slot assignment
> 
> Some devices are not fast enough to differentiate between a
> fast-moving contact and a new contact. This problem cannot be fully
> resolved because information is truly missing, but it is possible
> to safe-guard against obvious mistakes by restricting movement with
> a maximum displacement.
> 
> The new problem formulation for dmax > 0 cannot benefit from the
> speedup for positive definite matrices, but since the convergence is
> faster, the result is about the same. For a handful of contacts, the
> latency difference is truly negligible.
> 
> Suggested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
> ---
>  drivers/input/input-mt.c                  | 31 ++++++++++++++++++++-----------
>  drivers/input/mouse/alps.c                |  2 +-
>  drivers/input/mouse/bcm5974.c             |  2 +-
>  drivers/input/mouse/cypress_ps2.c         |  2 +-
>  drivers/input/mouse/synaptics.c           |  2 +-
>  drivers/input/touchscreen/pixcir_i2c_ts.c |  2 +-
>  include/linux/input/mt.h                  |  3 ++-
>  7 files changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
> index fbe29fc..cb150a1 100644
> --- a/drivers/input/input-mt.c
> +++ b/drivers/input/input-mt.c
> @@ -293,7 +293,7 @@ void input_mt_sync_frame(struct input_dev *dev)
>  }
>  EXPORT_SYMBOL(input_mt_sync_frame);
>  
> -static int adjust_dual(int *begin, int step, int *end, int eq)
> +static int adjust_dual(int *begin, int step, int *end, int eq, int mu)
>  {
>  	int f, *p, s, c;
>  
> @@ -311,9 +311,10 @@ static int adjust_dual(int *begin, int step, int *end, int eq)
>  			s = *p;
>  
>  	c = (f + s + 1) / 2;
> -	if (c == 0 || (c > 0 && !eq))
> +	if (c == 0 || (c > mu && (!eq || mu > 0)))
>  		return 0;
> -	if (s < 0)
> +	/* Improve convergence for positive matrices by penalizing overcovers */
> +	if (s < 0 && mu <= 0)
>  		c *= 2;
>  
>  	for (p = begin; p != end; p += step)
> @@ -322,23 +323,24 @@ static int adjust_dual(int *begin, int step, int *end, int eq)
>  	return (c < s && s <= 0) || (f >= 0 && f < c);
>  }
>  
> -static void find_reduced_matrix(int *w, int nr, int nc, int nrc)
> +static void find_reduced_matrix(int *w, int nr, int nc, int nrc, int mu)
>  {
>  	int i, k, sum;
>  
>  	for (k = 0; k < nrc; k++) {
>  		for (i = 0; i < nr; i++)
> -			adjust_dual(w + i, nr, w + i + nrc, nr <= nc);
> +			adjust_dual(w + i, nr, w + i + nrc, nr <= nc, mu);
>  		sum = 0;
>  		for (i = 0; i < nrc; i += nr)
> -			sum += adjust_dual(w + i, 1, w + i + nr, nc <= nr);
> +			sum += adjust_dual(w + i, 1, w + i + nr, nc <= nr, mu);
>  		if (!sum)
>  			break;
>  	}
>  }
>  
>  static int input_mt_set_matrix(struct input_mt *mt,
> -			       const struct input_mt_pos *pos, int num_pos)
> +			       const struct input_mt_pos *pos, int num_pos,
> +			       int mu)
>  {
>  	const struct input_mt_pos *p;
>  	struct input_mt_slot *s;
> @@ -352,7 +354,7 @@ static int input_mt_set_matrix(struct input_mt *mt,
>  		y = input_mt_get_value(s, ABS_MT_POSITION_Y);
>  		for (p = pos; p != pos + num_pos; p++) {
>  			int dx = x - p->x, dy = y - p->y;
> -			*w++ = dx * dx + dy * dy;
> +			*w++ = dx * dx + dy * dy - mu;
>  		}
>  	}
>  
> @@ -393,17 +395,24 @@ static void input_mt_set_slots(struct input_mt *mt,
>   * @slots: the slot assignment to be filled
>   * @pos: the position array to match
>   * @num_pos: number of positions
> + * @dmax: maximum ABS_MT_POSITION displacement (zero for infinite)
>   *
>   * Performs a best match against the current contacts and returns
>   * the slot assignment list. New contacts are assigned to unused
>   * slots.
>   *
> + * The assignments are balanced so that all coordinate displacements are
> + * below the euclidian distance dmax. If no such assignment can be found,
> + * some contacts are assigned to unused slots.
> + *
>   * Returns zero on success, or negative error in case of failure.
>   */
>  int input_mt_assign_slots(struct input_dev *dev, int *slots,
> -			  const struct input_mt_pos *pos, int num_pos)
> +			  const struct input_mt_pos *pos, int num_pos,
> +			  int dmax)
>  {
>  	struct input_mt *mt = dev->mt;
> +	int mu = 2 * dmax * dmax;
>  	int nrc;
>  
>  	if (!mt || !mt->red)
> @@ -413,8 +422,8 @@ int input_mt_assign_slots(struct input_dev *dev, int *slots,
>  	if (num_pos < 1)
>  		return 0;
>  
> -	nrc = input_mt_set_matrix(mt, pos, num_pos);
> -	find_reduced_matrix(mt->red, num_pos, nrc / num_pos, nrc);
> +	nrc = input_mt_set_matrix(mt, pos, num_pos, mu);
> +	find_reduced_matrix(mt->red, num_pos, nrc / num_pos, nrc, mu);
>  	input_mt_set_slots(mt, slots, num_pos);
>  
>  	return 0;
> diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
> index 54ff0379..6c64fb2 100644
> --- a/drivers/input/mouse/alps.c
> +++ b/drivers/input/mouse/alps.c
> @@ -435,7 +435,7 @@ static void alps_report_mt_data(struct psmouse *psmouse, int n)
>  	struct alps_fields *f = &priv->f;
>  	int i, slot[MAX_TOUCHES];
>  
> -	input_mt_assign_slots(dev, slot, f->mt, n);
> +	input_mt_assign_slots(dev, slot, f->mt, n, 0);
>  	for (i = 0; i < n; i++)
>  		alps_set_slot(dev, slot[i], f->mt[i].x, f->mt[i].y);
>  
> diff --git a/drivers/input/mouse/bcm5974.c b/drivers/input/mouse/bcm5974.c
> index c329cdb..b10709f 100644
> --- a/drivers/input/mouse/bcm5974.c
> +++ b/drivers/input/mouse/bcm5974.c
> @@ -564,7 +564,7 @@ static int report_tp_state(struct bcm5974 *dev, int size)
>  		dev->index[n++] = &f[i];
>  	}
>  
> -	input_mt_assign_slots(input, dev->slots, dev->pos, n);
> +	input_mt_assign_slots(input, dev->slots, dev->pos, n, 0);
>  
>  	for (i = 0; i < n; i++)
>  		report_finger_data(input, dev->slots[i],
> diff --git a/drivers/input/mouse/cypress_ps2.c b/drivers/input/mouse/cypress_ps2.c
> index 8af34ff..9118a18 100644
> --- a/drivers/input/mouse/cypress_ps2.c
> +++ b/drivers/input/mouse/cypress_ps2.c
> @@ -538,7 +538,7 @@ static void cypress_process_packet(struct psmouse *psmouse, bool zero_pkt)
>  		pos[i].y = contact->y;
>  	}
>  
> -	input_mt_assign_slots(input, slots, pos, n);
> +	input_mt_assign_slots(input, slots, pos, n, 0);
>  
>  	for (i = 0; i < n; i++) {
>  		contact = &report_data.contacts[i];
> diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
> index f947292..84d0401 100644
> --- a/drivers/input/mouse/synaptics.c
> +++ b/drivers/input/mouse/synaptics.c
> @@ -1204,7 +1204,7 @@ static void synaptics_profile_sensor_process(struct psmouse *psmouse,
>  		pos[i].y = synaptics_invert_y(hw[i]->y);
>  	}
>  
> -	input_mt_assign_slots(dev, slot, pos, nsemi);
> +	input_mt_assign_slots(dev, slot, pos, nsemi, 0);
>  
>  	for (i = 0; i < nsemi; i++) {
>  		input_mt_slot(dev, slot[i]);
> diff --git a/drivers/input/touchscreen/pixcir_i2c_ts.c b/drivers/input/touchscreen/pixcir_i2c_ts.c
> index fc49c75..ccdf654 100644
> --- a/drivers/input/touchscreen/pixcir_i2c_ts.c
> +++ b/drivers/input/touchscreen/pixcir_i2c_ts.c
> @@ -126,7 +126,7 @@ static void pixcir_ts_report(struct pixcir_i2c_ts_data *ts,
>  			pos[i].y = touch->y;
>  		}
>  
> -		input_mt_assign_slots(ts->input, slots, pos, n);
> +		input_mt_assign_slots(ts->input, slots, pos, n, 0);
>  	}
>  
>  	for (i = 0; i < n; i++) {
> diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
> index f583ff6..d7188de 100644
> --- a/include/linux/input/mt.h
> +++ b/include/linux/input/mt.h
> @@ -119,7 +119,8 @@ struct input_mt_pos {
>  };
>  
>  int input_mt_assign_slots(struct input_dev *dev, int *slots,
> -			  const struct input_mt_pos *pos, int num_pos);
> +			  const struct input_mt_pos *pos, int num_pos,
> +			  int dmax);
>  
>  int input_mt_get_slot_by_key(struct input_dev *dev, int key);
>  
> -- 
> 2.2.2
>