staging: iio: resolver: ad2s1210: refactor setting excitation frequency

This combines the ad2s1210_update_frequency_control_word() and
ad2s1210_soft_reset() functions into a single function since they
both have to be called together. (The software reset does not reset
any configuration registers, it only updates the excitation output
and resets the tracking loop.)

Also clean up a few things while touching this:
- move AD2S1210_DEF_EXCIT macro with similar macros
- remove unnecessary dev_err() calls
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20230929-ad2s1210-mainline-v3-15-fa4364281745@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1210.c

@@ -51,12 +51,11 @@
 #define AD2S1210_MIN_CLKIN	6144000
 #define AD2S1210_MAX_CLKIN	10240000
 #define AD2S1210_MIN_EXCIT	2000
+#define AD2S1210_DEF_EXCIT	10000
 #define AD2S1210_MAX_EXCIT	20000
 #define AD2S1210_MIN_FCW	0x4
 #define AD2S1210_MAX_FCW	0x50
 
-#define AD2S1210_DEF_EXCIT	10000
-
 enum ad2s1210_mode {
 	MOD_POS = 0b00,
 	MOD_VEL = 0b01,
@@ -189,18 +188,32 @@ static int ad2s1210_regmap_reg_read(void *context, unsigned int reg,
 	return 0;
 }
 
-static inline
-int ad2s1210_update_frequency_control_word(struct ad2s1210_state *st)
+/*
+ * Sets the excitation frequency and performs software reset.
+ *
+ * Must be called with lock held.
+ */
+static int ad2s1210_reinit_excitation_frequency(struct ad2s1210_state *st,
+						u16 fexcit)
 {
-	unsigned char fcw;
+	int ret;
+	u8 fcw;
 
-	fcw = (unsigned char)(st->fexcit * (1 << 15) / st->clkin_hz);
-	if (fcw < AD2S1210_MIN_FCW || fcw > AD2S1210_MAX_FCW) {
-		dev_err(&st->sdev->dev, "ad2s1210: FCW out of range\n");
+	fcw = fexcit * (1 << 15) / st->clkin_hz;
+	if (fcw < AD2S1210_MIN_FCW || fcw > AD2S1210_MAX_FCW)
 		return -ERANGE;
-	}
 
-	return regmap_write(st->regmap, AD2S1210_REG_EXCIT_FREQ, fcw);
+	ret = regmap_write(st->regmap, AD2S1210_REG_EXCIT_FREQ, fcw);
+	if (ret < 0)
+		return ret;
+
+	st->fexcit = fexcit;
+
+	/*
+	 * Software reset reinitializes the excitation frequency output.
+	 * It does not reset any of the configuration registers.
+	 */
+	return regmap_write(st->regmap, AD2S1210_REG_SOFT_RESET, 0);
 }
 
 static int ad2s1210_set_resolution_gpios(struct ad2s1210_state *st,
@@ -215,11 +228,6 @@ static int ad2s1210_set_resolution_gpios(struct ad2s1210_state *st,
 				     bitmap);
 }
 
-static inline int ad2s1210_soft_reset(struct ad2s1210_state *st)
-{
-	return regmap_write(st->regmap, AD2S1210_REG_SOFT_RESET, 0);
-}
-
 static ssize_t ad2s1210_show_fexcit(struct device *dev,
 				    struct device_attribute *attr,
 				    char *buf)
@@ -234,27 +242,24 @@ static ssize_t ad2s1210_store_fexcit(struct device *dev,
 				     const char *buf, size_t len)
 {
 	struct ad2s1210_state *st = iio_priv(dev_to_iio_dev(dev));
-	unsigned int fexcit;
+	u16 fexcit;
 	int ret;
 
-	ret = kstrtouint(buf, 10, &fexcit);
-	if (ret < 0)
-		return ret;
-	if (fexcit < AD2S1210_MIN_EXCIT || fexcit > AD2S1210_MAX_EXCIT) {
-		dev_err(dev,
-			"ad2s1210: excitation frequency out of range\n");
+	ret = kstrtou16(buf, 10, &fexcit);
+	if (ret < 0 || fexcit < AD2S1210_MIN_EXCIT || fexcit > AD2S1210_MAX_EXCIT)
 		return -EINVAL;
-	}
+
 	mutex_lock(&st->lock);
-	st->fexcit = fexcit;
-	ret = ad2s1210_update_frequency_control_word(st);
+	ret = ad2s1210_reinit_excitation_frequency(st, fexcit);
 	if (ret < 0)
 		goto error_ret;
-	ret = ad2s1210_soft_reset(st);
+
+	ret = len;
+
 error_ret:
 	mutex_unlock(&st->lock);
 
-	return ret < 0 ? ret : len;
+	return ret;
 }
 
 static ssize_t ad2s1210_show_resolution(struct device *dev,
@@ -551,10 +556,8 @@ static int ad2s1210_initial(struct ad2s1210_state *st)
 	if (ret < 0)
 		goto error_ret;
 
-	ret = ad2s1210_update_frequency_control_word(st);
-	if (ret < 0)
-		goto error_ret;
-	ret = ad2s1210_soft_reset(st);
+	ret = ad2s1210_reinit_excitation_frequency(st, AD2S1210_DEF_EXCIT);
+
 error_ret:
 	mutex_unlock(&st->lock);
 	return ret;
@@ -698,7 +701,6 @@ static int ad2s1210_probe(struct spi_device *spi)
 	st->sdev = spi;
 	st->hysteresis = true;
 	st->resolution = 12;
-	st->fexcit = AD2S1210_DEF_EXCIT;
 
 	ret = ad2s1210_setup_clocks(st);
 	if (ret < 0)