linux-kernel - RE: [PATCH] Input: elantench - Fix the firmware misreport coordinates for trackpoint occasionally.

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Date:   Fri, 10 Sep 2021 10:18:08 +0800
From:   "phoenix" <phoenix@....com.tw>
To:     "'Dmitry Torokhov'" <dmitry.torokhov@...il.com>
Cc:     <linux-kernel@...r.kernel.org>, <linux-input@...r.kernel.org>,
        <jingle.wu@....com.tw>, <josh.chen@....com.tw>,
        <dave.wang@....com.tw>
Subject: RE: [PATCH] Input: elantench - Fix the firmware misreport coordinates for trackpoint occasionally.

Hi Dmity,

Sorry for late reply.
> +		if (packet[4] == 0x80 || packet[5] == 0x80 ||
> +		    packet[1] >> 7 == packet[4] >> 7 ||
"I think this will reject X coordinates in range [0, 127]. Is this really
what is needed? What kind of patterns are you observing when firmware
misreports coordinates?"
this will reject X in range [128, 256] and [-128, -256]. This patch prevent
cursor suddenly jump to screen edge or corner.
The patterns we observing as below:
1. x (packet[4]) or y (packet[5]) is 0x80, ex: [xx xx xx xx 80 80]
2. ~x sign bit is same as MSB(most significant bit) of x, ex: [30 00 00 06
00 00] 
3. ~y sign bit is same as MSB of y, ex: [30 00 00 06 fa 00]

Best regards,
Phoenix Huang
-----Original Message-----
From: Dmitry Torokhov [mailto:dmitry.torokhov@...il.com] 
Sent: Tuesday, August 31, 2021 4:24 AM
To: phoenix <phoenix@....com.tw>
Cc: linux-kernel@...r.kernel.org; linux-input@...r.kernel.org;
jingle.wu@....com.tw; josh.chen@....com.tw; dave.wang@....com.tw
Subject: Re: [PATCH] Input: elantench - Fix the firmware misreport
coordinates for trackpoint occasionally.

Hi Phoenix,

On Mon, Aug 30, 2021 at 08:19:48PM +0800, phoenix wrote:
> Hi Dmitry,
> 
> Would you review this patch, thanks
> 
> Best regards,
> Phoenix Huang
> 
> -----Original Message-----
> From: Phoenix Huang [mailto:phoenix@....com.tw]
> Sent: Thursday, July 29, 2021 9:10 AM
> To: linux-kernel@...r.kernel.org; linux-input@...r.kernel.org; 
> dmitry.torokhov@...il.com
> Cc: jingle.wu@....com.tw; josh.chen@....com.tw; dave.wang@....com.tw; 
> Phoenix Huang <phoenix@....com.tw>
> Subject: [PATCH] Input: elantench - Fix the firmware misreport 
> coordinates for trackpoint occasionally.
> 
> Signed-off-by: Phoenix Huang <phoenix@....com.tw>
> ---
>  drivers/input/mouse/elantech.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/input/mouse/elantech.c 
> b/drivers/input/mouse/elantech.c index 2d0bc029619f..07e1098f2d31 
> 100644
> --- a/drivers/input/mouse/elantech.c
> +++ b/drivers/input/mouse/elantech.c
> @@ -517,6 +517,17 @@ static void elantech_report_trackpoint(struct 
> psmouse *psmouse,
>  	case 0x16008020U:
>  	case 0x26800010U:
>  	case 0x36808000U:
> +	
> +		/* This firmware misreport coordinates for trackpoint
> occasionally.
> +		* So we discard these packets by pattern to prevent cursor
> jumps.
> +		*/
> +		if (packet[4] == 0x80 || packet[5] == 0x80 ||
> +		    packet[1] >> 7 == packet[4] >> 7 ||

I think this will reject X coordinates in range [0, 127]. Is this really
what is needed? What kind of patterns are you observing when firmware
misreports coordinates?

Thanks.

--
Dmitry