iio: trigger: stm32-timer: fix get/set down count direction

Fixes: 4adec7da0536 ("iio: stm32 trigger: Add quadrature encoder device")

This fixes two issues:
- stm32_set_count_direction: to set down direction
- stm32_get_count_direction: to get down direction

IIO core provides/expects value to be an index of iio_enum items array.
This needs to be turned by these routines into TIM_CR1_DIR (e.g. BIT(4))
value.
Also, report error when attempting to write direction, when in encoder
mode: in this case, direction is read only (given by encoder inputs).

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/trigger/stm32-timer-trigger.c

@@ -594,13 +594,20 @@ static const char *const stm32_count_direction_states[] = {
 
 static int stm32_set_count_direction(struct iio_dev *indio_dev,
 				     const struct iio_chan_spec *chan,
-				     unsigned int mode)
+				     unsigned int dir)
 {
 	struct stm32_timer_trigger *priv = iio_priv(indio_dev);
+	u32 val;
+	int mode;
 
-	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_DIR, mode);
+	/* In encoder mode, direction is RO (given by TI1/TI2 signals) */
+	regmap_read(priv->regmap, TIM_SMCR, &val);
+	mode = (val & TIM_SMCR_SMS) - 1;
+	if ((mode >= 0) || (mode < ARRAY_SIZE(stm32_quadrature_modes)))
+		return -EBUSY;
 
-	return 0;
+	return regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_DIR,
+				  dir ? TIM_CR1_DIR : 0);
 }
 
 static int stm32_get_count_direction(struct iio_dev *indio_dev,
@@ -611,7 +618,7 @@ static int stm32_get_count_direction(struct iio_dev *indio_dev,
 
 	regmap_read(priv->regmap, TIM_CR1, &cr1);
 
-	return (cr1 & TIM_CR1_DIR);
+	return ((cr1 & TIM_CR1_DIR) ? 1 : 0);
 }
 
 static const struct iio_enum stm32_count_direction_enum = {