Re: [PATCH v3 1/] iio: proximity: lidar: optimize i2c transactions

[Jonathan Cameron <jic23@kernel.org>]

On 02/12/15 05:05, Matt Ranostay wrote:
> Optimize device tranactions using i2c transfers versus multiple
> possibly racey i2c_smbus_* function calls, and only one transaction
> for distance measurement. Falls back to smbus method if i2c
> functionality isn't available.
> 
> Signed-off-by: Matt Ranostay <mranostay@gmail.com>
This ended up more fiddly that I expected, but seems like you got
it right to me.

Applied to the togreg branch of iio.git - initially pushed out as
testing for the autobuilders to play with it.

Jonathan
> ---
>  drivers/iio/proximity/pulsedlight-lidar-lite-v2.c | 95 +++++++++++++++++------
>  1 file changed, 70 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c b/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> index 32f24f1..05db6ce 100644
> --- a/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> +++ b/drivers/iio/proximity/pulsedlight-lidar-lite-v2.c
> @@ -36,8 +36,10 @@
>  #define LIDAR_REG_STATUS_INVALID	BIT(3)
>  #define LIDAR_REG_STATUS_READY		BIT(0)
>  
> -#define LIDAR_REG_DATA_HBYTE	0x0f
> -#define LIDAR_REG_DATA_LBYTE	0x10
> +#define LIDAR_REG_DATA_HBYTE		0x0f
> +#define LIDAR_REG_DATA_LBYTE		0x10
> +#define LIDAR_REG_DATA_WORD_READ	BIT(7)
> +
>  #define LIDAR_REG_PWR_CONTROL	0x65
>  
>  #define LIDAR_DRV_NAME "lidar"
> @@ -46,6 +48,9 @@ struct lidar_data {
>  	struct iio_dev *indio_dev;
>  	struct i2c_client *client;
>  
> +	int (*xfer)(struct lidar_data *data, u8 reg, u8 *val, int len);
> +	int i2c_enabled;
> +
>  	u16 buffer[8]; /* 2 byte distance + 8 byte timestamp */
>  };
>  
> @@ -64,7 +69,28 @@ static const struct iio_chan_spec lidar_channels[] = {
>  	IIO_CHAN_SOFT_TIMESTAMP(1),
>  };
>  
> -static int lidar_read_byte(struct lidar_data *data, int reg)
> +static int lidar_i2c_xfer(struct lidar_data *data, u8 reg, u8 *val, int len)
> +{
> +	struct i2c_client *client = data->client;
> +	struct i2c_msg msg[2];
> +	int ret;
> +
> +	msg[0].addr = client->addr;
> +	msg[0].flags = client->flags | I2C_M_STOP;
> +	msg[0].len = 1;
> +	msg[0].buf  = (char *) &reg;
> +
> +	msg[1].addr = client->addr;
> +	msg[1].flags = client->flags | I2C_M_RD;
> +	msg[1].len = len;
> +	msg[1].buf = (char *) val;
> +
> +	ret = i2c_transfer(client->adapter, msg, 2);
> +
> +	return (ret == 2) ? 0 : ret;
> +}
> +
> +static int lidar_smbus_xfer(struct lidar_data *data, u8 reg, u8 *val, int len)
>  {
>  	struct i2c_client *client = data->client;
>  	int ret;
> @@ -74,17 +100,35 @@ static int lidar_read_byte(struct lidar_data *data, int reg)
>  	 * so in turn i2c_smbus_read_byte_data cannot be used
>  	 */
>  
> -	ret = i2c_smbus_write_byte(client, reg);
> -	if (ret < 0) {
> -		dev_err(&client->dev, "cannot write addr value");
> -		return ret;
> +	while (len--) {
> +		ret = i2c_smbus_write_byte(client, reg++);
> +		if (ret < 0) {
> +			dev_err(&client->dev, "cannot write addr value");
> +			return ret;
> +		}
> +
> +		ret = i2c_smbus_read_byte(client);
> +		if (ret < 0) {
> +			dev_err(&client->dev, "cannot read data value");
> +			return ret;
> +		}
> +
> +		*(val++) = ret;
>  	}
>  
> -	ret = i2c_smbus_read_byte(client);
> +	return 0;
> +}
> +
> +static int lidar_read_byte(struct lidar_data *data, u8 reg)
> +{
> +	int ret;
> +	u8 val;
> +
> +	ret = data->xfer(data, reg, &val, 1);
>  	if (ret < 0)
> -		dev_err(&client->dev, "cannot read data value");
> +		return ret;
>  
> -	return ret;
> +	return val;
>  }
>  
>  static inline int lidar_write_control(struct lidar_data *data, int val)
> @@ -100,22 +144,14 @@ static inline int lidar_write_power(struct lidar_data *data, int val)
>  
>  static int lidar_read_measurement(struct lidar_data *data, u16 *reg)
>  {
> -	int ret;
> -	int val;
> -
> -	ret = lidar_read_byte(data, LIDAR_REG_DATA_HBYTE);
> -	if (ret < 0)
> -		return ret;
> -	val = ret << 8;
> +	int ret = data->xfer(data, LIDAR_REG_DATA_HBYTE |
> +			(data->i2c_enabled ? LIDAR_REG_DATA_WORD_READ : 0),
> +			(u8 *) reg, 2);
>  
> -	ret = lidar_read_byte(data, LIDAR_REG_DATA_LBYTE);
> -	if (ret < 0)
> -		return ret;
> +	if (!ret)
> +		*reg = be16_to_cpu(*reg);
>  
> -	val |= ret;
> -	*reg = val;
> -
> -	return 0;
> +	return ret;
>  }
>  
>  static int lidar_get_measurement(struct lidar_data *data, u16 *reg)
> @@ -237,6 +273,16 @@ static int lidar_probe(struct i2c_client *client,
>  	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
>  	if (!indio_dev)
>  		return -ENOMEM;
> +	data = iio_priv(indio_dev);
> +
> +	if (i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
> +		data->xfer = lidar_i2c_xfer;
> +		data->i2c_enabled = 1;
> +	} else if (i2c_check_functionality(client->adapter,
> +				I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_BYTE))
> +		data->xfer = lidar_smbus_xfer;
> +	else
> +		return -ENOTSUPP;
>  
>  	indio_dev->info = &lidar_info;
>  	indio_dev->name = LIDAR_DRV_NAME;
> @@ -244,7 +290,6 @@ static int lidar_probe(struct i2c_client *client,
>  	indio_dev->num_channels = ARRAY_SIZE(lidar_channels);
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  
> -	data = iio_priv(indio_dev);
>  	i2c_set_clientdata(client, indio_dev);
>  
>  	data->client = client;
>