Message-ID: <332E958ABC555E44B6FC413E3DFEAA3D3C2AD90A7C@VMBX131.ihostexchange.net>
Date:	Wed, 28 Sep 2011 19:50:05 -0400
From:	Kevin McNeely <kev@...ress.com>
To:	Javier Martinez Canillas <martinez.javier@...il.com>,
	Henrik Rydberg <rydberg@...omail.se>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH V3 1/3] Input: cyttsp - Cypress TTSP capacitive
 multi-touch screen support

Hi Javier,

Yes, the hardware reports touches in the range 1 to 14.

Best regards,
Kevin


> -----Original Message-----
> From: Javier Martinez Canillas [mailto:martinez.javier@...il.com]
> Sent: Wednesday, September 28, 2011 4:23 PM
> To: Henrik Rydberg
> Cc: Dmitry Torokhov; Greg Kroah-Hartman; linux-input@...r.kernel.org;
> linux-kernel@...r.kernel.org; Kevin McNeely
> Subject: Re: [PATCH V3 1/3] Input: cyttsp - Cypress TTSP capacitive multi-
> touch screen support
>
> On Tue, Sep 27, 2011 at 1:52 PM, Henrik Rydberg <rydberg@...omail.se>
> wrote:
> > Hi Javier,
> >
> >> Cypress TrueTouch(tm) Standard Product controllers are found in a
> >> wide range of embedded devices. This driver add support for a variety
> >> of TTSP controllers.
> >
> > please find some comments below.
> >
>
> Hello Henrik,
>
> Thanks a lot for the review
>
> >> +/* Slots management */
> >> +#define CY_MAX_FINGER               4 #define CY_UNUSED
> >> +0 #define CY_USED                     1
> >
> > These two look like bool, please use as bool instead.
> >
> >> +#define CY_MAX_ID                   15
> >
> > Why not 16 here?
> >
>
> Because as far as I know there are only 14 possible tracking ids (1-14), not 16.
> 15 and 0 are not valid track ids.
>
> When a contact lifts off the hardware reports a magic number (15) for it.
> Also, the sequence always start with 1 which is the track id that gets the first
> contact reported by the touch.
>
> >> +
> >> +/* TrueTouch Standard Product Gen3 interface definition */ struct
> >> +cyttsp_xydata {
> >> +     u8 hst_mode;
> >> +     u8 tt_mode;
> >> +     u8 tt_stat;
> >> +     struct cyttsp_tch tch1;
> >> +     u8 touch12_id;
> >> +     struct cyttsp_tch tch2;
> >> +     u8 gest_cnt;
> >> +     u8 gest_id;
> >> +     struct cyttsp_tch tch3;
> >> +     u8 touch34_id;
> >> +     struct cyttsp_tch tch4;
> >> +     u8 tt_undef[3];
> >> +     u8 act_dist;
> >> +     u8 tt_reserved;
> >> +} __packed;
> >
> > Too bad the touches are not an array here...
> >
>
> Yes, the problem is that the offset between touches is not uniform.
> For tch1 and tch2 is only 8 bits but the offset between tch2 and tch3 is 16 (u8
> * 2) for example.
>
> >> +     int slot_curr[CY_MAX_ID];
> >> +     int slot_prev[CY_MAX_ID];
> >
> > These two are not needed; the input core will take care of duplicates,
> > so slot_prev can be removed. Also, the set of current slots can be
> > tracked using a temporary bitmask, so slot_curr can be removed as well.
>
> Perfect, I'll remove both. I didn't know that the input core took care of
> duplicates, sorry for not getting this from the docs.
>
> >> +
> >> +static void cyttsp_get_tch(struct cyttsp_xydata *xy_data, int idx,
> >> +                        struct cyttsp_tch **tch) {
> >> +     switch (idx) {
> >> +     case 0:
> >> +             *tch = &xy_data->tch1;
> >> +             break;
> >> +     case 1:
> >> +             *tch = &xy_data->tch2;
> >> +             break;
> >> +     case 2:
> >> +             *tch = &xy_data->tch3;
> >> +             break;
> >> +     case 3:
> >> +             *tch = &xy_data->tch4;
> >> +             break;
> >> +     }
> >> +}
> >
> > How about returning a const struct cyttsp_tch* here instead.
> >
>
> Ok, will return a struct pointer instead.
>
> >> +
> >> +     cyttsp_extract_track_ids(&xy_data, ids);
> >> +
> >> +     for (i = 0; i < num_cur_tch; i++) {
> >> +             ts->slot_curr[ids[i] - 1] = CY_USED;
> >
> > Why the -1 here? Since the values are provably between 0 and 15, there
> > is no need to change them further.
>
> As I told you before is a HW thing. I looked at the track ids reported by the
> touchscreen and their values are always between 1 and 14. So I did the -1 to
> avoid having and unused element in the array. (I don't have the HW
> datasheet so maybe I'm wrong with this)
>
> Kevin?
>
> >
> > Also, the above line could be replaced by "used |= 1 << ids[i]", for instance.
> >
> >> +
> >> +             cyttsp_get_tch(&xy_data, i, &tch);
> >> +
> >> +             x = be16_to_cpu(tch->x);
> >> +             y = be16_to_cpu(tch->y);
> >> +             z = tch->z;
> >> +
> >> +             cyttsp_report_slot(ts->input, ids[i] - 1, x, y, z);
> >
> > Ditto, -1.
> >
> >> +     }
> >> +
> >> +     for (i = 0; i < CY_MAX_ID; i++) {
> >> +             if (ts->slot_prev[i] == CY_USED &&
> >> +                 ts->slot_curr[i] == CY_UNUSED)
> >> +                     cyttsp_report_slot_empty(ts->input, i);
> >> +             ts->slot_prev[i] = ts->slot_curr[i];
> >> +             ts->slot_curr[i] = CY_UNUSED;
> >> +     }
> >
> > Input core handles duplicate calls, so the above could be simplified.
> >
>
> Perfect, will clean this code.
>
> >> +
> >> +     for (i = 0; i < CY_MAX_ID; i++) {
> >> +             ts->slot_prev[i] = CY_UNUSED;
> >> +             ts->slot_curr[i] = CY_UNUSED;
> >> +     }
> >
> > Could be removed.
> >
>
> Yes, I'll do that.
>
> >
> > Thanks,
> > Henrik
> >
>
> Thanks for your comments, I will work on these issues and resubmit a new
> version of the patch-set.
>
> Best regards,
>
> --
> Javier Martínez Canillas
> (+34) 682 39 81 69
> Barcelona, Spain

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