i2c/tsl2550: Use combined SMBus transactions

Make the I/O faster, mainly by using combined SMBus transactions when
possible. While the TSL2550 datasheet doesn't say the device supports
them, they seem to work just fine in practice, and a combined
transaction is faster than two simple transactions in many cases and
always more reliable.

A side effect is to suppress the delays between SMBus writes and
reads. The datasheet doesn't say they are needed and things work just
fine for me without them.

I also couldn't see any reason for the delay between reading the two
channels. Nor for the loop to get a reading in the first place. The
400 ms delay between samples only matters at chip power-up, after that
the chip always hold the previously sampled value so we never get to
wait.

All these changes make reading the lux value much faster and cheaper.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Michele De Candia <michele.decandia@valueteam.com>
Cc: Rodolfo Giometti <giometti@linux.it>

diff --git a/drivers/i2c/chips/tsl2550.c b/drivers/i2c/chips/tsl2550.c
index b96f302..aa96bd2 100644 (file)
--- a/drivers/i2c/chips/tsl2550.c
+++ b/drivers/i2c/chips/tsl2550.c
@@ -24,10 +24,9 @@
 #include <linux/slab.h>
 #include <linux/i2c.h>
 #include <linux/mutex.h>
-#include <linux/delay.h>
 
 #define TSL2550_DRV_NAME       "tsl2550"
-#define DRIVER_VERSION         "1.1.2"
+#define DRIVER_VERSION         "1.2"
 
 /*
  * Defines
@@ -96,32 +95,13 @@ static int tsl2550_set_power_state(struct i2c_client *client, int state)
 
 static int tsl2550_get_adc_value(struct i2c_client *client, u8 cmd)
 {
-       unsigned long end;
-       int loop = 0, ret = 0;
+       int ret;
 
-       /*
-        * Read ADC channel waiting at most 400ms (see data sheet for further
-        * info).
-        * To avoid long busy wait we spin for few milliseconds then
-        * start sleeping.
-        */
-       end = jiffies + msecs_to_jiffies(400);
-       while (time_before(jiffies, end)) {
-               i2c_smbus_write_byte(client, cmd);
-
-               if (loop++ < 5)
-                       mdelay(1);
-               else
-                       msleep(1);
-
-               ret = i2c_smbus_read_byte(client);
-               if (ret < 0)
-                       return ret;
-               else if (ret & 0x0080)
-                       break;
-       }
+       ret = i2c_smbus_read_byte_data(client, cmd);
+       if (ret < 0)
+               return ret;
        if (!(ret & 0x80))
-               return -EIO;
+               return -EAGAIN;
        return ret & 0x7f;      /* remove the "valid" bit */
 }
 
@@ -285,8 +265,6 @@ static ssize_t __tsl2550_show_lux(struct i2c_client *client, char *buf)
                return ret;
        ch0 = ret;
 
-       mdelay(1);
-
        ret = tsl2550_get_adc_value(client, TSL2550_READ_ADC1);
        if (ret < 0)
                return ret;
@@ -345,11 +323,10 @@ static int tsl2550_init_client(struct i2c_client *client)
         * Probe the chip. To do so we try to power up the device and then to
         * read back the 0x03 code
         */
-       err = i2c_smbus_write_byte(client, TSL2550_POWER_UP);
+       err = i2c_smbus_read_byte_data(client, TSL2550_POWER_UP);
        if (err < 0)
                return err;
-       mdelay(1);
-       if (i2c_smbus_read_byte(client) != TSL2550_POWER_UP)
+       if (err != TSL2550_POWER_UP)
                return -ENODEV;
        data->power_state = 1;
 
@@ -374,7 +351,8 @@ static int __devinit tsl2550_probe(struct i2c_client *client,
        struct tsl2550_data *data;
        int *opmode, err = 0;
 
-       if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE)) {
+       if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE
+                                           | I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
                err = -EIO;
                goto exit;
        }