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

Dmitry Torokhov
2011-08-18T07:52:34Z

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@gmail.com> 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@emc.com.tw>
> > > ---
> > > 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