Commit ac780941 authored by Jean Delvare's avatar Jean Delvare
Browse files

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: default avatarJean Delvare <khali@linux-fr.org>
Tested-by: default avatarMichele De Candia <michele.decandia@valueteam.com>
Cc: Rodolfo Giometti <giometti@linux.it>
parent 27693ce5

drivers/i2c/chips/tsl2550.c

+10 −32
Original line number Diff line number Diff line
@@ -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;



	/*

	 * 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);

	int ret;



		ret = i2c_smbus_read_byte(client);

	ret = i2c_smbus_read_byte_data(client, cmd);

	if (ret < 0)

		return ret;

		else if (ret & 0x0080)

			break;

	}

	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;

	}

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