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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>
This commit is contained in:
Jean Delvare 2009-09-18 22:45:44 +02:00
parent 27693ce5f3
commit ac7809414f
1 changed files with 10 additions and 32 deletions
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42
drivers/i2c/chips/tsl2550.c
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@ -24,10 +24,9 @@
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/i2c.h> #include <linux/i2c.h>
#include <linux/mutex.h> #include <linux/mutex.h>
#include <linux/delay.h>
#define TSL2550_DRV_NAME "tsl2550" #define TSL2550_DRV_NAME "tsl2550"
#define DRIVER_VERSION "1.1.2" #define DRIVER_VERSION "1.2"
/* /*
* Defines * 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) static int tsl2550_get_adc_value(struct i2c_client *client, u8 cmd)
{ {
unsigned long end; int ret;
int loop = 0, ret = 0;
/* ret = i2c_smbus_read_byte_data(client, cmd);
* Read ADC channel waiting at most 400ms (see data sheet for further if (ret < 0)
* info). return ret;
* 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;
}
if (!(ret & 0x80)) if (!(ret & 0x80))
return -EIO; return -EAGAIN;
return ret & 0x7f; /* remove the "valid" bit */ 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; return ret;
ch0 = ret; ch0 = ret;
mdelay(1);
ret = tsl2550_get_adc_value(client, TSL2550_READ_ADC1); ret = tsl2550_get_adc_value(client, TSL2550_READ_ADC1);
if (ret < 0) if (ret < 0)
return ret; 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 * Probe the chip. To do so we try to power up the device and then to
* read back the 0x03 code * 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) if (err < 0)
return err; return err;
mdelay(1); if (err != TSL2550_POWER_UP)
if (i2c_smbus_read_byte(client) != TSL2550_POWER_UP)
return -ENODEV; return -ENODEV;
data->power_state = 1; data->power_state = 1;
@ -374,7 +351,8 @@ static int __devinit tsl2550_probe(struct i2c_client *client,
struct tsl2550_data *data; struct tsl2550_data *data;
int *opmode, err = 0; 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; err = -EIO;
goto exit; goto exit;
} }