iio: accel: bma220: make suspend state setting more robust

The datasheet mentions that the suspend mode is toggled by reading the
suspend register. The reading returns value 0xFF if the system was in
suspend mode, otherwise it returns value 0x00.

The bma220_deinit() function does up to 2 reads, in case the device was in
suspend mode, which suggests a level of paranoia that makes the logic in
bma220_suspend() and bma220_resume() look insufficient.

This change implements a bma220_power() function which does up to 2 reads
of the suspend register to make sure that the chip enters a desired
(suspended or normal) mode.

If the transition fails, then -EBUSY is returned.

Since only a reference to SPI device is required, we can remove the
spi_set_drvdata() call and get the SPI device object from the base device
object in the suspend/resume routines.
Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210625140137.362282-2-aardelean@deviqon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/bma220_spi.c

@@ -218,14 +218,33 @@ static int bma220_init(struct spi_device *spi)
 	return 0;
 }
 
-static void bma220_deinit(void *spi)
+static int bma220_power(struct spi_device *spi, bool up)
 {
-	int ret;
+	int i, ret;
+
+	/**
+	 * The chip can be suspended/woken up by a simple register read.
+	 * So, we need up to 2 register reads of the suspend register
+	 * to make sure that the device is in the desired state.
+	 */
+	for (i = 0; i < 2; i++) {
+		ret = bma220_read_reg(spi, BMA220_REG_SUSPEND);
+		if (ret < 0)
+			return ret;
 
-	/* Make sure the chip is powered off */
-	ret = bma220_read_reg(spi, BMA220_REG_SUSPEND);
-	if (ret == BMA220_SUSPEND_SLEEP)
-		bma220_read_reg(spi, BMA220_REG_SUSPEND);
+		if (up && ret == BMA220_SUSPEND_SLEEP)
+			return 0;
+
+		if (!up && ret == BMA220_SUSPEND_WAKE)
+			return 0;
+	}
+
+	return -EBUSY;
+}
+
+static void bma220_deinit(void *spi)
+{
+	bma220_power(spi, false);
 }
 
 static int bma220_probe(struct spi_device *spi)
@@ -242,7 +261,6 @@ static int bma220_probe(struct spi_device *spi)
 
 	data = iio_priv(indio_dev);
 	data->spi_device = spi;
-	spi_set_drvdata(spi, indio_dev);
 	mutex_init(&data->lock);
 
 	indio_dev->info = &bma220_info;
@@ -273,17 +291,16 @@ static int bma220_probe(struct spi_device *spi)
 
 static __maybe_unused int bma220_suspend(struct device *dev)
 {
-	struct bma220_data *data = iio_priv(dev_get_drvdata(dev));
+	struct spi_device *spi = to_spi_device(dev);
 
-	/* The chip can be suspended/woken up by a simple register read. */
-	return bma220_read_reg(data->spi_device, BMA220_REG_SUSPEND);
+	return bma220_power(spi, false);
 }
 
 static __maybe_unused int bma220_resume(struct device *dev)
 {
-	struct bma220_data *data = iio_priv(dev_get_drvdata(dev));
+	struct spi_device *spi = to_spi_device(dev);
 
-	return bma220_read_reg(data->spi_device, BMA220_REG_SUSPEND);
+	return bma220_power(spi, true);
 }
 static SIMPLE_DEV_PM_OPS(bma220_pm_ops, bma220_suspend, bma220_resume);