Re: [PATCH] input: s6sy761: fix coordinate read bit shift
From: Andi Shyti <hidden>
Date: 2021-03-05 14:25:39
Also in:
lkml, phone-devel
Hi Caleb,
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256
Please clean up the commit message.
The touch coordinates are read by shifting a value left by 3, this is incorrect and effectively causes the coordinates to be half of the correct value. Shift by 4 bits instead to report the correct value. This matches downstream examples, and has been confirmed on my device (OnePlus 7 Pro).
The real reason is that from the register we get:
byte 3 byte 2 byte 1
+--------+--------+ +-----------------+ +-----------------+
| | | | | | |
| X[3:0] | Y[3:0] | | Y[11:4] | | X[11:4] |
| | | | | | |
+--------+--------+ +-----------------+ +-----------------+
and the 12 bit values have to fit in a 16bit variable.
The upper 8 bits (in event[2] and event[1] need to be shifted
left by '4' and not by '3' in order to leave space to the lower
4 bits (in event[3]).
quoted hunk ↗ jump to hunk
Signed-off-by: Caleb Connolly <redacted> --- drivers/input/touchscreen/s6sy761.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)diff --git a/drivers/input/touchscreen/s6sy761.c b/drivers/input/touchscreen/s6sy761.c index b63d7fdf0cd2..85a1f465c097 100644 --- a/drivers/input/touchscreen/s6sy761.c +++ b/drivers/input/touchscreen/s6sy761.c@@ -145,8 +145,8 @@ static void s6sy761_report_coordinates(struct s6sy761_data *sdata, u8 major = event[4]; u8 minor = event[5]; u8 z = event[6] & S6SY761_MASK_Z; - u16 x = (event[1] << 3) | ((event[3] & S6SY761_MASK_X) >> 4); - u16 y = (event[2] << 3) | (event[3] & S6SY761_MASK_Y); + u16 x = (event[1] << 4) | ((event[3] & S6SY761_MASK_X) >> 4); + u16 y = (event[2] << 4) | (event[3] & S6SY761_MASK_Y);
the devil knows how that '3' has ended up there :) Thanks for catching it! Reviewed-by: Andi Shyti <redacted> Andi