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Date:   Sun, 7 Nov 2021 22:06:30 -0800
From:   Dmitry Torokhov <dmitry.torokhov@gmail.com>
To:     Yufei Du <yufeidu@cs.unc.edu>
Cc:     linux-kernel@vger.kernel.org, linux-input@vger.kernel.org,
        jingle.wu@emc.com.tw, josh.chen@emc.com.tw, dave.wang@emc.com.tw,
        phoenix <phoenix@emc.com.tw>
Subject: Re: [PATCH] Input: elantench - Fix the firmware misreport
 coordinates for trackpoint occasionally.
Message-ID: <YYi+ZoeGtFO+/HYO@google.com>
References: <20210729010940.5752-1-phoenix@emc.com.tw>
 <000001d79d99$53762dd0$fa628970$@emc.com.tw>
 <YS0+TU21/nok6Ge9@google.com>
 <3a98b10e-6b78-b769-e22d-2496d7bcd69d@cs.unc.edu>
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Hi Yufei,

On Sun, Nov 07, 2021 at 03:02:27PM -0500, Yufei Du wrote:
> Hi Dmitry,
> 
> I am a user currently suffering from the firmware bug that causes my
> trackpoint to be unusable on my Lenovo X13 Gen 1 AMD. I tested this patch in
> the latest 5.15 mainline kernel tree and can possibly answer your questions
> regarding the patch.
> 
> > I think this will reject X coordinates in range [0, 127]. Is this really
> > what is needed?
> 
> As Phoenix explained in his reply, the patch will reject X and Y coordinates
> larger than 127 or smaller than -127. This is because the most significant
> bit of packet[1] (for X) and packet[2] (for Y) are inverse of the sign bit.
> Although I do not have the formal design specification of the device, I
> tried pushing the trackpoint as hard as I could, and the X and Y coordinates
> never go beyond +/-127 normally, so I believe that this patch would not
> cause any functionality issue.
> 
> > What kind of patterns are you observing when firmware
> > misreports coordinates?
> 
> Here is a sample log I observed (with elantech.debug set to 2 for more
> debugging messages):
> psmouse serio1: elantech: PS/2 packet [10 00 80 26 f9 0a]
> psmouse serio1: elantech: PS/2 packet [10 00 80 26 00 80]
> psmouse serio1: elantech: PS/2 packet [10 00 80 00 00 00]
> psmouse serio1: Touchpad at isa0060/serio1/input0 lost sync at byte 6
> psmouse serio1: elantech: PS/2 packet [10 00 80 26 f8 0b]
> psmouse serio1: Touchpad at isa0060/serio1/input0 - driver resynced.
> 
> The first packet is a valid packet. The second packet is the incorrect
> packet that this patch prevents. The third packet is a corrupted packet that
> psmouse detects (as shown in the "lost sync" message), and the fourth packet
> is a valid packet again. Without the patch, the second packet would cause
> the cursor to jump to the edge of the screen.
> 
> So far, all my logs of this issue show the same pattern of a jumpy incorrect
> packet followed by a corrupted packet that causes psmouse to lose sync.
> There are more logs and discussions in the BugZilla entry here:
> https://bugzilla.kernel.org/show_bug.cgi?id=209167
> 
> Hope my explanation helped a bit.

Sorry I lost track of this patch. Can I add your Tested-by to it before
applying?

Thanks.

-- 
Dmitry