linux-kernel - Re: [PATCH 2/4] HID: wiiu-drc: Implement touch reports

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Date:   Thu, 6 May 2021 12:20:12 +0200
From:   Emmanuel Gil Peyrot <linkmauve@...kmauve.fr>
To:     Jonathan Neuschäfer <j.ne@...teo.net>
Cc:     Emmanuel Gil Peyrot <linkmauve@...kmauve.fr>,
        linux-input@...r.kernel.org, Ash Logan <ash@...quark.com>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] HID: wiiu-drc: Implement touch reports

On Wed, May 05, 2021 at 10:43:55PM +0000, Jonathan Neuschäfer wrote:
> Hi,
> 
> some more comments below. Enjoy :)
> 
> On Mon, May 03, 2021 at 01:28:33AM +0200, Emmanuel Gil Peyrot wrote:
> > There is a 100×200 inaccessible border on each side, and the Y axis is
> > inverted, these are the two main quirks of this touch panel.
> 
> Does that mean 100 px borders left and right, and 200 px borders top and
> bottom?

Correct, I’ll reformulate in v2. :)

> 
> 100×200 evokes the image of a rectangle of that size, which I found
> confusing for a moment.
> 
> > 
> > I’ve been testing with weston-simple-touch mostly, but it also with the
> > rest of Weston.
> > 
> > Signed-off-by: Ash Logan <ash@...quark.com>
> > Signed-off-by: Emmanuel Gil Peyrot <linkmauve@...kmauve.fr>
> > ---
> >  drivers/hid/hid-wiiu-drc.c | 83 +++++++++++++++++++++++++++++++++++---
> >  1 file changed, 78 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/hid/hid-wiiu-drc.c b/drivers/hid/hid-wiiu-drc.c
> > index 018cbdb53a2c..77e70827c37d 100644
> > --- a/drivers/hid/hid-wiiu-drc.c
> > +++ b/drivers/hid/hid-wiiu-drc.c
> > @@ -49,13 +49,27 @@
> >  
> >  #define BUTTON_POWER	BIT(25)
> >  
> > +/* Touch constants */
> > +/* Resolution in pixels */
> > +#define RES_X		854
> > +#define RES_Y		480
> > +/* Display/touch size in mm */
> > +#define WIDTH		138
> > +#define HEIGHT		79
> > +#define NUM_TOUCH_POINTS 10
> > +#define MAX_TOUCH_RES	(1 << 12)
> > +#define TOUCH_BORDER_X	100
> > +#define TOUCH_BORDER_Y	200
> 
> [...]
> > +	/* touch */
> > +	/* Average touch points for improved accuracy. */
> > +	x = y = 0;
> > +	for (i = 0; i < NUM_TOUCH_POINTS; i++) {
> > +		base = 36 + 4 * i;
> > +
> > +		x += ((data[base + 1] & 0xF) << 8) | data[base];
> > +		y += ((data[base + 3] & 0xF) << 8) | data[base + 2];
> > +	}
> > +	x /= NUM_TOUCH_POINTS;
> > +	y /= NUM_TOUCH_POINTS;
> 
> Given that there are 10 possible touch points: Does the gamepad actually
> support multitouch (usefully)?
> 
> If so, I think it would be better to report all touch points
> individually to userspace, to allow for multitouch gestures;
> userspace can still implement averaging if desired.

Sadly no, in my testing all ten reports are always within a few units
from each other, even if I press two (or more) different points on the
touchscreen at the same time.

My guess would be, the firmware and report format got written before
Nintendo decided whether to go for a capacitive or resistive touch
panel, and they didn’t get changed once the final decision was made to
go for a non-multitouch-aware resistive panel.

I’ll add some factual comment about this in v2.

> 
> 
> 
> Thanks,
> Jonathan

Thanks!

-- 
Emmanuel Gil Peyrot

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