linux-kernel - [PATCH v2] input: s6sy761: fix coordinate read bit shift

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Message-ID: <20210305185710.225168-1-caleb@connolly.tech>
Date:   Fri, 05 Mar 2021 18:58:10 +0000
From:   Caleb Connolly <caleb@...nolly.tech>
To:     caleb@...nolly.tech, andi@...zian.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh@...nel.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] input: s6sy761: fix coordinate read bit shift

The touch coordinate register contains the following:

        byte 3             byte 2             byte 1
+--------+--------+ +-----------------+ +-----------------+
|        |        | |                 | |                 |
| X[3:0] | Y[3:0] | |     Y[11:4]     | |     X[11:4]     |
|        |        | |                 | |                 |
+--------+--------+ +-----------------+ +-----------------+

Bytes 2 and 1 need to be shifted left by 4 bits, the least significant
nibble of each is stored in byte 3. Currently they are only
being shifted by 3 causing the reported coordinates to be incorrect.

This matches downstream examples, and has been confirmed on my
device (OnePlus 7 Pro).

Fixes: 0145a7141e59 ("Input: add support for the Samsung S6SY761
touchscreen")
Signed-off-by: Caleb Connolly <caleb@...nolly.tech>
---
Changes since v1:
 * Use Andi's explanation in the commit message
 * Add Fixes: tag

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