leds: turris-omnia: Fix brightness setting and trigger activating

I have improperly refactored commits
4d5ed2621c24 ("leds: turris-omnia: Make set_brightness() more efficient")
and
aaf38273cf76 ("leds: turris-omnia: Support HW controlled mode via private trigger")
after Lee requested a change in API semantics of the new functions I
introduced in commit
28350bc0ac77 ("leds: turris-omnia: Do not use SMBUS calls").

Before the change, the function omnia_cmd_write_u8() returned 0 on
success, and afterwards it returned a positive value (number of bytes
written). The latter version was applied, but the following commits did
not properly account for this change.

This results in non-functional LED's .brightness_set_blocking() and
trigger's .activate() methods.

The main reasoning behind the semantics change was that read/write
methods should return the number of read/written bytes on success.
It was pointed to me [1] that this is not always true (for example the
regmap API does not do so), and since the driver never uses this number
of read/written bytes information, I decided to fix this issue by
changing the functions to the original semantics (return 0 on success).

[1] https://lore.kernel.org/linux-gpio/[e-mail]/

Fixes: 28350bc0ac77 ("leds: turris-omnia: Do not use SMBUS calls")
Signed-off-by: Marek Behún <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/leds-turris-omnia.c

···
 static int omnia_cmd_write_u8(const struct i2c_client *client, u8 cmd, u8 val)
 {
 	u8 buf[2] = { cmd, val };
+	int ret;
 
-	return i2c_master_send(client, buf, sizeof(buf));
+	ret = i2c_master_send(client, buf, sizeof(buf));
+
+	return ret < 0 ? ret : 0;
 }
 
 static int omnia_cmd_read_raw(struct i2c_adapter *adapter, u8 addr, u8 cmd,
···
 
 	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
 	if (likely(ret == ARRAY_SIZE(msgs)))
-		return len;
+		return 0;
 	else if (ret < 0)
 		return ret;
 	else
···
 static int omnia_cmd_read_u8(const struct i2c_client *client, u8 cmd)
 {
 	u8 reply;
-	int ret;
+	int err;
 
-	ret = omnia_cmd_read_raw(client->adapter, client->addr, cmd, &reply, 1);
-	if (ret < 0)
-		return ret;
+	err = omnia_cmd_read_raw(client->adapter, client->addr, cmd, &reply, 1);
+	if (err)
+		return err;
 
 	return reply;
 }
···
 
 	mutex_unlock(&leds->lock);
 
-	if (err < 0)
+	if (err)
 		dev_err(cdev->dev, "Cannot put LED to software mode: %i\n",
 			err);
 }
···
 	ret = omnia_cmd_write_u8(client, CMD_LED_MODE,
 				 CMD_LED_MODE_LED(led->reg) |
 				 CMD_LED_MODE_USER);
-	if (ret < 0) {
+	if (ret) {
 		dev_err(dev, "Cannot set LED %pOF to software mode: %i\n", np,
 			ret);
 		return ret;
···
 	/* disable the LED */
 	ret = omnia_cmd_write_u8(client, CMD_LED_STATE,
 				 CMD_LED_STATE_LED(led->reg));
-	if (ret < 0) {
+	if (ret) {
 		dev_err(dev, "Cannot set LED %pOF brightness: %i\n", np, ret);
 		return ret;
 	}
···
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	unsigned long brightness;
-	int ret;
+	int err;
 
 	if (kstrtoul(buf, 10, &brightness))
 		return -EINVAL;
···
 	if (brightness > 100)
 		return -EINVAL;
 
-	ret = omnia_cmd_write_u8(client, CMD_LED_SET_BRIGHTNESS, brightness);
+	err = omnia_cmd_write_u8(client, CMD_LED_SET_BRIGHTNESS, brightness);
 
-	return ret < 0 ? ret : count;
+	return err ?: count;
 }
 static DEVICE_ATTR_RW(brightness);
 
···
 	struct i2c_client *client = to_i2c_client(dev);
 	struct omnia_leds *leds = i2c_get_clientdata(client);
 	bool val;
-	int ret;
+	int err;
 
 	if (!leds->has_gamma_correction)
 		return -EOPNOTSUPP;
···
 	if (kstrtobool(buf, &val) < 0)
 		return -EINVAL;
 
-	ret = omnia_cmd_write_u8(client, CMD_SET_GAMMA_CORRECTION, val);
+	err = omnia_cmd_write_u8(client, CMD_SET_GAMMA_CORRECTION, val);
 
-	return ret < 0 ? ret : count;
+	return err ?: count;
 }
 static DEVICE_ATTR_RW(gamma_correction);
 
···
 
 	err = omnia_cmd_read_raw(client->adapter, OMNIA_MCU_I2C_ADDR,
 				 CMD_GET_STATUS_WORD, &reply, sizeof(reply));
-	if (err < 0)
+	if (err)
 		return err;
 
 	/* Check whether MCU firmware supports the CMD_GET_FEAUTRES command */
···
 
 	err = omnia_cmd_read_raw(client->adapter, OMNIA_MCU_I2C_ADDR,
 				 CMD_GET_FEATURES, &reply, sizeof(reply));
-	if (err < 0)
+	if (err)
 		return err;
 
 	return le16_to_cpu(reply);