[PATCH] iio: gyro: mpu3050: restore cached sample rate on runtime resume

[Herman van Hazendonk <github.com@herrie.org>]

mpu3050_runtime_resume() only calls mpu3050_power_up(), which clears
the SLEEP bit and waits 200 ms for the chip's register file to come
back. It does not reprogram the full-scale, low-pass filter or sample
rate divisor, all of which return to the chip's power-on defaults
across a power cycle.

The driver's cached state (mpu3050->fullscale, mpu3050->lpf,
mpu3050->divisor) is the source of truth for what userspace observes
through the IIO ABI: in_anglvel_sampling_frequency goes through
mpu3050_get_freq() which reads the cached lpf and divisor, and
in_anglvel_scale similarly reads cached fullscale. After the first
autosuspend cycle the chip's actual sample rate diverges from what
sysfs reports, until the next IIO_CHAN_INFO_RAW read incidentally
reprograms the chip via mpu3050_set_8khz_samplerate() and the cached
state restoration paths in mpu3050_fifo_read_one().

That incidental restoration is only triggered by direct sysfs raw
reads, not by buffered/triggered mode. A user who configures the
sample rate, starts buffered capture and then leaves the device idle
long enough to autosuspend will see chip-default-rate samples after
resume rather than the configured rate.

Reprogram the chip from the cached state in mpu3050_runtime_resume()
by calling mpu3050_start_sampling() after mpu3050_power_up() succeeds.
On failure power the chip back down to keep regulator and pm_runtime
reference counts in sync with the error path.

Fixes: 3904b28efb2c ("iio: gyro: Add driver for the MPU-3050 gyroscope")
Signed-off-by: Herman van Hazendonk <github.com@herrie.org>
---
 drivers/iio/gyro/mpu3050-core.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/gyro/mpu3050-core.c b/drivers/iio/gyro/mpu3050-core.c
index d84e04e4b431..ac041074cfdf 100644
--- a/drivers/iio/gyro/mpu3050-core.c
+++ b/drivers/iio/gyro/mpu3050-core.c
@@ -1291,7 +1291,32 @@ static int mpu3050_runtime_suspend(struct device *dev)
 
 static int mpu3050_runtime_resume(struct device *dev)
 {
-	return mpu3050_power_up(iio_priv(dev_get_drvdata(dev)));
+	struct mpu3050 *mpu3050 = iio_priv(dev_get_drvdata(dev));
+	int ret;
+
+	ret = mpu3050_power_up(mpu3050);
+	if (ret)
+		return ret;
+
+	/*
+	 * mpu3050_power_up() only clears the SLEEP bit; it leaves the
+	 * full-scale, low-pass filter and sample rate divisor at the
+	 * chip's power-on defaults. Restore them from the driver's
+	 * cached state so the hardware matches what userspace observes
+	 * via the IIO ABI (in_anglvel_sampling_frequency, in_anglvel_scale)
+	 * across a suspend/resume cycle. Without this the chip continues
+	 * to deliver samples at chip-default rate after the first
+	 * autosuspend cycle, until the next IIO_CHAN_INFO_RAW read
+	 * incidentally reprograms it.
+	 */
+	ret = mpu3050_start_sampling(mpu3050);
+	if (ret) {
+		dev_err(dev, "failed to restore sampling config on resume\n");
+		mpu3050_power_down(mpu3050);
+		return ret;
+	}
+
+	return 0;
 }
 
 DEFINE_RUNTIME_DEV_PM_OPS(mpu3050_dev_pm_ops, mpu3050_runtime_suspend,
-- 
2.43.0