linux-kernel - Re: [PATCH v2 1/3] hid-multitouch: add support for trackpads

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Message-ID: <20120120164849.GA6520@core.coreip.homeip.net>
Date:	Fri, 20 Jan 2012 08:48:49 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Benjamin Tissoires <benjamin.tissoires@...c.fr>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>,
	Mohamed Ikbel Boulabiar <boulabiar@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] hid-multitouch: add support for trackpads

On Fri, Jan 20, 2012 at 05:09:48PM +0100, Henrik Rydberg wrote:
> Hi Benjamin,
> 
> > @@ -389,9 +404,19 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
> >  				td->last_field_index = field->index;
> >  			return -1;
> >  		}
> > +		case HID_DG_TOUCH:
> > +			/* Legacy devices use TIPSWITCH and not TOUCH.
> > +			 * Let's just ignore this field. */
> > +			return -1;
> >  		/* let hid-input decide for the others */
> >  		return 0;
> >  
> > +	case HID_UP_BUTTON:
> > +		code = ((usage->hid - 1) & HID_USAGE) + BTN_MOUSE;
> 
> Why '+' here instead of '|' is  beyond me...

Because it is an offset for the range. The fact that it is on power 2
boundary and we can use "|" is purely coincidential here.

Maybe we should even write it as:

		code = BTN_MOUSE + ((usage->hid - 1) & HID_USAGE);

Thanks,
Dmitry

-- 
Dmitry
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