[PATCH 1/2] hwmon/tmp401: use smb word operations instead of 2 smb byte operations

From: <jeroen.de_wachter.ext@nokia.com>
To: <linux@roeck-us.net>, <jdelvare@suse.com>
Cc: <linux-hwmon@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	Jeroen De Wachter <jeroen.de_wachter.ext@nokia.com>
Subject: [PATCH 1/2] hwmon/tmp401: use smb word operations instead of 2 smb byte operations
Date: Mon, 9 Jan 2017 17:47:37 +0100	[thread overview]
Message-ID: <1483980458-28202-1-git-send-email-jeroen.de_wachter.ext@nokia.com> (raw)

From: Jeroen De Wachter <jeroen.de_wachter.ext@nokia.com>

tmp401 separately read/wrote high and low bytes of temperature values while
the hardware supports reading/writing those values in one operation. Driver
has been modified to use word operations where possible.

Tested with a tmp432 sensor on a mips64 platform.

Signed-off-by: Jeroen De Wachter <jeroen.de_wachter.ext@nokia.com>
---
 drivers/hwmon/tmp401.c | 48 +++++++++++++++++++++++++++++-------------------
 1 file changed, 29 insertions(+), 19 deletions(-)

diff --git a/drivers/hwmon/tmp401.c b/drivers/hwmon/tmp401.c
index eeeed2c..88b17e4 100644
--- a/drivers/hwmon/tmp401.c
+++ b/drivers/hwmon/tmp401.c
@@ -213,25 +213,29 @@ static int tmp401_update_device_reg16(struct i2c_client *client,
 	for (i = 0; i < num_sensors; i++) {		/* local / r1 / r2 */
 		for (j = 0; j < num_regs; j++) {	/* temp / low / ... */
 			u8 regaddr;
-			/*
-			 * High byte must be read first immediately followed
-			 * by the low byte
-			 */
+
 			regaddr = data->kind == tmp432 ?
 						TMP432_TEMP_MSB_READ[j][i] :
 						TMP401_TEMP_MSB_READ[j][i];
-			val = i2c_smbus_read_byte_data(client, regaddr);
-			if (val < 0)
-				return val;
-			data->temp[j][i] = val << 8;
-			if (j == 3)		/* crit is msb only */
-				continue;
-			regaddr = data->kind == tmp432 ? TMP432_TEMP_LSB[j][i]
-						       : TMP401_TEMP_LSB[j][i];
-			val = i2c_smbus_read_byte_data(client, regaddr);
+			if (j == 3) { /* crit is msb only */
+				val = i2c_smbus_read_byte_data(client, regaddr);
+			} else {
+				/*
+				 * Hardware provides big endian data. However,
+				 * the smbus protocol expects the LSB first in
+				 * I2C_SMBUS_WORD_DATA operations.
+				 * i2c_smbus_read_word_swapped swaps the bytes
+				 * in the value it receives from
+				 * i2c_smbus_read_word_data before returning the
+				 * data, so we get the correct value.
+				 */
+				val = i2c_smbus_read_word_swapped(client,
+								  regaddr);
+			}
 			if (val < 0)
 				return val;
-			data->temp[j][i] |= val;
+
+			data->temp[j][i] = j == 3 ? val << 8 : val;
 		}
 	}
 	return 0;
@@ -373,11 +377,17 @@ static ssize_t store_temp(struct device *dev, struct device_attribute *devattr,
 
 	regaddr = data->kind == tmp432 ? TMP432_TEMP_MSB_WRITE[nr][index]
 				       : TMP401_TEMP_MSB_WRITE[nr][index];
-	i2c_smbus_write_byte_data(client, regaddr, reg >> 8);
-	if (nr != 3) {
-		regaddr = data->kind == tmp432 ? TMP432_TEMP_LSB[nr][index]
-					       : TMP401_TEMP_LSB[nr][index];
-		i2c_smbus_write_byte_data(client, regaddr, reg & 0xFF);
+	if (nr == 3) { /* crit is msb only */
+		i2c_smbus_write_byte_data(client, regaddr, reg >> 8);
+	} else {
+		/*
+		 * Hardware expects big endian data. However, the smbus protocol
+		 * puts the LSB first in I2C_SMBUS_WORD_DATA operations.
+		 * i2c_smbus_write_word_data_swapped will swap the bytes before
+		 * passing them to i2c_smbus_write_word_data, so the hardware
+		 * will receive the MSB first, as expected.
+		 */
+		i2c_smbus_write_word_swapped(client, regaddr, reg);
 	}
 	data->temp[nr][index] = reg;
 
-- 
1.8.3.1
