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

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Message-ID: <20110818063818.GC10093@core.coreip.homeip.net>
Date:	Wed, 17 Aug 2011 23:38:18 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	JJ Ding <jj_ding@....com.tw>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Seth Forshee <seth.forshee@...onical.com>,
	Aaron Huang <aaron_huang@....com.tw>,
	Tom Lin <tom_lin@....com.tw>,
	Eric Piel <E.A.B.Piel@...elft.nl>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Chase Douglas <chase.douglas@...onical.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Alessandro Rubini <rubini@...l.unipv.it>
Subject: Re: [PATCH 3/6] Input: elantech - packet checking for v2 hardware

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@....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;
> +
> +	if ((packet[0] & 0xc0) == 0x80)
> +		return (packet[0] & 0x0c) == 0x0c &&
> +		       (packet[3] & 0x0e) == 0x08;
> +
> +	return (packet[0] & 0x3c) == 0x3c &&
> +	       (packet[1] & 0xf0) == 0x00 &&
> +	       (packet[3] & 0x3e) == 0x38 &&
> +	       (packet[4] & 0xf0) == 0x00;

Can we please spell out the assumptions under which we decide that
packet is invalid?

Thanks.

-- 
Dmitry
--
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