iio: st_sensors: add debugfs register read hook

This adds a debugfs hook to read/write registers in the ST
sensors using debugfs. Proved to be awesome help when trying
to debug why IRQs do not arrive.

Signed-off-by: Linus Walleij <[e-mail]>
Acked-by: Denis Ciocca <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/accel/st_accel_core.c

···
 	.attrs = &st_accel_attribute_group,
 	.read_raw = &st_accel_read_raw,
 	.write_raw = &st_accel_write_raw,
+	.debugfs_reg_access = &st_sensors_debugfs_reg_access,
 };
 
 #ifdef CONFIG_IIO_TRIGGER

drivers/iio/common/st_sensors/st_sensors_core.c

···
 	return err;
 }
 
+int st_sensors_debugfs_reg_access(struct iio_dev *indio_dev,
+				  unsigned reg, unsigned writeval,
+				  unsigned *readval)
+{
+	struct st_sensor_data *sdata = iio_priv(indio_dev);
+	u8 readdata;
+	int err;
+
+	if (!readval)
+		return sdata->tf->write_byte(&sdata->tb, sdata->dev,
+					     (u8)reg, (u8)writeval);
+
+	err = sdata->tf->read_byte(&sdata->tb, sdata->dev, (u8)reg, &readdata);
+	if (err < 0)
+		return err;
+
+	*readval = (unsigned)readdata;
+
+	return 0;
+}
+EXPORT_SYMBOL(st_sensors_debugfs_reg_access);
+
 static int st_sensors_match_odr(struct st_sensor_settings *sensor_settings,
 			unsigned int odr, struct st_sensor_odr_avl *odr_out)
 {

drivers/iio/gyro/st_gyro_core.c

···
 	.attrs = &st_gyro_attribute_group,
 	.read_raw = &st_gyro_read_raw,
 	.write_raw = &st_gyro_write_raw,
+	.debugfs_reg_access = &st_sensors_debugfs_reg_access,
 };
 
 #ifdef CONFIG_IIO_TRIGGER

drivers/iio/magnetometer/st_magn_core.c

···
 	.attrs = &st_magn_attribute_group,
 	.read_raw = &st_magn_read_raw,
 	.write_raw = &st_magn_write_raw,
+	.debugfs_reg_access = &st_sensors_debugfs_reg_access,
 };
 
 #ifdef CONFIG_IIO_TRIGGER

drivers/iio/pressure/st_pressure_core.c

···
 	.attrs = &st_press_attribute_group,
 	.read_raw = &st_press_read_raw,
 	.write_raw = &st_press_write_raw,
+	.debugfs_reg_access = &st_sensors_debugfs_reg_access,
 };
 
 #ifdef CONFIG_IIO_TRIGGER

include/linux/iio/common/st_sensors.h

···
 
 void st_sensors_power_disable(struct iio_dev *indio_dev);
 
+int st_sensors_debugfs_reg_access(struct iio_dev *indio_dev,
+				  unsigned reg, unsigned writeval,
+				  unsigned *readval);
+
 int st_sensors_set_odr(struct iio_dev *indio_dev, unsigned int odr);
 
 int st_sensors_set_dataready_irq(struct iio_dev *indio_dev, bool enable);