[PATCH] input: s6sy761: fix coordinate read bit shift

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

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).

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);
 
 	input_mt_slot(sdata->input, tid);
 

-- 
2.29.2


-----BEGIN PGP SIGNATURE-----
Version: ProtonMail
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=hTKj
-----END PGP SIGNATURE-----

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]).

the devil knows how that '3' has ended up there :)

Thanks for catching it!

Reviewed-by: Andi Shyti <redacted>

Andi

Hi Andi,

On 05/03/2021 11:55 am, Andi Shyti wrote:

Hi Caleb,

quoted

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Please clean up the commit message.

oops! Sorry

quoted

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]).

Thanks for clarifying, sorry for my rather naive commit message.

quoted

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>

Regards,

Caleb

Andi