linux-kernel - [PATCH] iio: light: vcnl4000: Don't power on/off chip in config

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Message-ID: <20230907-vcnl4000-pm-fix-v1-1-58a11c1d5a6c@axis.com>
Date:   Thu, 7 Sep 2023 12:53:14 +0200
From:   Mårten Lindahl <marten.lindahl@...s.com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
CC:     <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...s.com>,
        Mårten Lindahl <marten.lindahl@...s.com>
Subject: [PATCH] iio: light: vcnl4000: Don't power on/off chip in config

After enabling/disabling interrupts on the vcnl4040 chip the als and/or
ps sensor is powered on or off depending on the interrupt enable bits.
This is made as a last step in write_event_config.

But there is no reason to do this as the runtime PM handles the power
state of the sensors. Interfering with this may impact sensor readings.

Consider the following:
 1. Userspace makes sensor data reading which triggers 2000ms RPM resume
    (sensor powered on) timeout
 2. Userspace disables interrupts => powers sensor off
 3. Userspace reads sensor data = 0 because sensor is off and RPM didn't
    power on the sensor as resume timeout is still active
 4. RPM resume timeout passed

Powering sensor off in (2) risks a time window of close to 2000ms where
sensor data readings are disabled as in (3).

Skip setting power state when writing new event config.

Signed-off-by: Mårten Lindahl <marten.lindahl@...s.com>
---
 drivers/iio/light/vcnl4000.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/iio/light/vcnl4000.c b/drivers/iio/light/vcnl4000.c
index 3a52b09c2823..fdf763a04b0b 100644
--- a/drivers/iio/light/vcnl4000.c
+++ b/drivers/iio/light/vcnl4000.c
@@ -1513,7 +1513,6 @@ static int vcnl4040_write_event_config(struct iio_dev *indio_dev,
 
 out:
 	mutex_unlock(&data->vcnl4000_lock);
-	data->chip_spec->set_power_state(data, data->ps_int || data->als_int);
 
 	return ret;
 }

---
base-commit: 7ba2090ca64ea1aa435744884124387db1fac70f
change-id: 20230907-vcnl4000-pm-fix-b58dc0dffb5c

Best regards,
-- 
Mårten Lindahl <marten.lindahl@...s.com>