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

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.

quoted

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.

quoted

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