[PATCH 5.15.y] Input: s6sy761 - fix resume ordering and restore sensing

[Sasha Levin <sashal@kernel.org>]

From: David Heidelberg <david@ixit.cz>

[ Upstream commit a215720959c5450b3699e243904b39c3f8f68888 ]

System suspend powers the controller off and resume powers it back on,
but the resume path enables the interrupt before s6sy761_power_on()
checks the boot. The firmware raises its boot-complete event on the
interrupt line, the threaded handler consumes it, s6sy761_power_on()
then reads an empty event and resume fails with -ENODEV, skipping the
touch function setup:

s6sy761 2-0048: PM: dpm_run_callback(): s6sy761_resume [s6sy761] returns -19

Power the chip on first and only then unmask the interrupt. Once resume
completes the boot handshake the chip comes back with sensing off, as
at probe where input_open() turns it on, so the touchscreen stays dead
after resume. Send SENSE_ON again when the input device is open.

Tested on a Pixel 3 XL over several s2idle cycles: resume succeeds and
the touch function and sense status match the pre-suspend state.

Assisted-by: LLM
Cc: stable@vger.kernel.org
Fixes: 0145a7141e59 ("Input: add support for the Samsung S6SY761 touchscreen")
Signed-off-by: David Heidelberg <david@ixit.cz>
Link: https://patch.msgid.link/20260926-s6sy761-suspend-v2-1-8f00a96ee6e8@ixit.cz
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[ sashal: Replaced guard(mutex) with explicit mutex_lock()/mutex_unlock() calls for C90 compatibility. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/input/touchscreen/s6sy761.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/input/touchscreen/s6sy761.c b/drivers/input/touchscreen/s6sy761.c
index 85a1f465c097e..6f1827cfc720d 100644
--- a/drivers/input/touchscreen/s6sy761.c
+++ b/drivers/input/touchscreen/s6sy761.c
@@ -510,10 +510,22 @@ static int __maybe_unused s6sy761_suspend(struct device *dev)
 static int __maybe_unused s6sy761_resume(struct device *dev)
 {
 	struct s6sy761_data *sdata = dev_get_drvdata(dev);
+	int err;
+
+	err = s6sy761_power_on(sdata);
+	if (err)
+		return err;
 
 	enable_irq(sdata->client->irq);
 
-	return s6sy761_power_on(sdata);
+	mutex_lock(&sdata->input->mutex);
+
+	if (input_device_enabled(sdata->input))
+		err = i2c_smbus_write_byte(sdata->client, S6SY761_SENSE_ON);
+
+	mutex_unlock(&sdata->input->mutex);
+
+	return err;
 }
 
 static const struct dev_pm_ops s6sy761_pm_ops = {
-- 
2.53.0