linux-kernel - Re: [PATCH v2 2/9] input: elants: support old touch report format

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Date:   Thu, 12 Dec 2019 20:45:52 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-kernel@...r.kernel.org, Henrik Rydberg <rydberg@...math.org>,
        James Chen <james.chen@....com.tw>,
        Johnny Chuang <johnny.chuang@....com.tw>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh-dt@...nel.org>,
        Scott Liu <scott.liu@....com.tw>
Subject: Re: [PATCH v2 2/9] input: elants: support old touch report format

On Thu, Dec 12, 2019 at 03:54:13AM +0300, Dmitry Osipenko wrote:
> 11.12.2019 19:03, Michał Mirosław пишет:
> > Support ELAN touchpad sensor with older firmware as found on eg. Asus
> > Transformer Pads.
[...]
> > @@ -814,8 +817,16 @@ static void elants_i2c_mt_event(struct elants_data *ts, u8 *buf)
> >  			pos = &buf[FW_POS_XY + i * 3];
> >  			x = (((u16)pos[0] & 0xf0) << 4) | pos[1];
> >  			y = (((u16)pos[0] & 0x0f) << 8) | pos[2];
> > -			p = buf[FW_POS_PRESSURE + i];
> > -			w = buf[FW_POS_WIDTH + i];
> > +			if (report_len == PACKET_SIZE_OLD) {
> > +				w = buf[FW_POS_WIDTH + i / 2];
> > +				w >>= 4 * (~i & 1);	// little-endian-nibbles
> > +				w |= w << 4;
> > +				w |= !w;
> > +				p = w;
> 
> Did you copy this from the downstream driver as-is? I'm looking at the
> Nexus 7 driver and it does the following for older format:
> 
> u8 size_idx[] = { 35, 35, 36, 36, 37, 37, 38, 38, 39, 39 };
> unsigned int s;
> 
> if (i & 1)
> 	s = buf[size_idx[i]];
> else
> 	s = buf[size_idx[i]] / 16;
> 
> w = s & 0xf;
> p = s * 16;

This is the same thing modulo (w), which is scaled here to declared axis
range (1-255 from 0-15, assuming 0 means "no touch" so it should not occur).

OTOH, I admit, that I don't have any software that can verify those
settings. It might be that eg. one of MT_PRESSURE or MT_TOUCH_MAJOR axes
should be dropped in this case, but with no docs I can't be sure what
the reported values really are.

This is from the original (GPL) code dump labeled 'Asus 10_6_1_27_5':

|  touch_size = ((i & 0x01) ? buf[size_index[i]] : (buf[size_index[i]] >> 4)) & 0x0F;
|  if(touch_size == 0) touch_size = 1;
|  if (touch_size <= 7)
|      touch_size = touch_size << 5;
|  else
|      touch_size = 255;
|    
|    input_report_abs(idev, ABS_MT_TOUCH_MAJOR, touch_size);
|    input_report_abs(idev, ABS_MT_PRESSURE, touch_size);


Best Regards,
Michał Mirosław