Re: [PATCH 3/6] Input: elantech - packet checking for v2 hardware

[Dmitry Torokhov]

On Thu, Aug 18, 2011 at 03:31:27PM +0800, JJ Ding wrote:
> Hi Dmitry,
> 
> On Wed, 17 Aug 2011 23:38:18 -0700, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote:
> > On Thu, Aug 18, 2011 at 09:57:06AM +0800, JJ Ding wrote:
> > > For v2 hardware, there is no real parity check, but we can still check
> > > some constant bits for data integrity.
> > > 
> > > Signed-off-by: JJ Ding <jj_ding@xxxxxxxxxx>
> > > ---
> > >  drivers/input/mouse/elantech.c |   26 +++++++++++++++++++++++---
> > >  1 files changed, 23 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
> > > index cf41f23..032181c 100644
> > > --- a/drivers/input/mouse/elantech.c
> > > +++ b/drivers/input/mouse/elantech.c
> > > @@ -376,6 +376,25 @@ static int elantech_check_parity_v1(struct psmouse *psmouse)
> > >  	       etd->parity[packet[3]] == p3;
> > >  }
> > >  
> > > +static int packet_simple_check_v2(struct psmouse *psmouse)
> > > +{
> > > +	struct elantech_data *etd = psmouse->private;
> > > +	unsigned char *packet = psmouse->packet;
> > > +
> > > +	if (etd->reports_pressure)
> > > +		return (packet[0] & 0x0c) == 0x04 &&
> > > +		       (packet[3] & 0x0f) == 0x02;
>         this is for newer v2 hardware
> 
> > > +
> > > +	if ((packet[0] & 0xc0) == 0x80)
> > > +		return (packet[0] & 0x0c) == 0x0c &&
> > > +		       (packet[3] & 0x0e) == 0x08;
>         this is for older v2, two finger touch 
> 
> > > +
> > > +	return (packet[0] & 0x3c) == 0x3c &&
> > > +	       (packet[1] & 0xf0) == 0x00 &&
> > > +	       (packet[3] & 0x3e) == 0x38 &&
> > > +	       (packet[4] & 0xf0) == 0x00;
>         this is for older v2, 1/3 finger touch
>       
> > 
> > Can we please spell out the assumptions under which we decide that
> > packet is invalid?
> > 
> > Thanks.
> > 
> > -- 
> > Dmitry
> V2 hardware has two flavors. Older ones that do not report pressure,
> and newer ones that reports pressure and width.
> 
> With newer ones, all packets (1, 2, 3 finger touch) have the same
> constant bits.
> 
> With older ones, 1/3 finger touch packets and 2 finger touch packets have
> different constant bits.
> 
> With all three cases, if the constant bits are not exactly what I
> expected, I consider them invalid.
> 
> Dmitry, how do you want me to improve this? not enough comments?

Right, if you could put the above into comments right in the
packet_simple_check_v2() that woudl be great.

Thanks.

-- 
Dmitry
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