linux-kernel - Re: [lm-sensors] [PATCH] hwmon: HIH-6130: Support I2C bus drivers without I2C_FUNC_SMBUS

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Message-ID: <52A7BFA4.2080402@roeck-us.net>
Date:	Tue, 10 Dec 2013 17:28:04 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	José Miguel Gonçalves 
	<jose.goncalves@...v.pt>, Jean Delvare <khali@...ux-fr.org>,
	Guenter Roeck <guenter.roeck@...csson.com>,
	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org
Subject: Re: [lm-sensors] [PATCH] hwmon: HIH-6130: Support I2C bus drivers
 without I2C_FUNC_SMBUS_QUICK

On 12/10/2013 04:57 PM, José Miguel Gonçalves wrote:
> Some I2C bus drivers do not allow zero-lenght data transfers which are

s/lenght/length/

> required to start a mesurement with the HIH6130/1 sensor. Nevertheless,

s/mesurement/measurement/

> we can overcome this limitation by writing a zero dummy byte. This byte
> is ignored by the sensor and was verified to be working with the OMAP
> I2C bus driver in a BeagleBone board.
>
> Signed-off-by: José Miguel Gonçalves <jose.goncalves@...v.pt>
> ---
>   drivers/hwmon/hih6130.c |   16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwmon/hih6130.c b/drivers/hwmon/hih6130.c
> index 2dc37c7..a860cc4 100644
> --- a/drivers/hwmon/hih6130.c
> +++ b/drivers/hwmon/hih6130.c
> @@ -121,8 +121,20 @@ static int hih6130_update_measurements(struct i2c_client *client)
>   	 */
>   	if (time_after(jiffies, hih6130->last_update + HZ) || !hih6130->valid) {
>
> -		/* write to slave address, no data, to request a measurement */
> -		ret = i2c_master_send(client, tmp, 0);
> +		/*
> +		 * Write to slave address, to request a measurement.

s/,//

> +		 * According with the datasheet it should be with no data, but
> +		 * for systems with I2C bus drivers that do not allow zero
> +		 * length packets we write one dummy byte to allow sensor
> +		 * measurements on them.
> +		 */
> +		if (i2c_get_functionality(client->adapter) &
> +		    I2C_FUNC_SMBUS_QUICK) {
> +			ret = i2c_master_send(client, tmp, 0);
> +		} else {
> +			tmp[0] = 0;
> +			ret = i2c_master_send(client, tmp, 1);
> +		}

You can simplify this code by introducing a variable to hold
the write length into struct hih6130. This variable can be
initialized with 1 or 0 in the probe function.

	if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_QUICK))
		hih6130->write_length = 0;
	else
		hih6130->write_length = 1;

Then replace above code with

	tmp[0] = 0;
	ret = i2c_master_send(client, tmp, hih6130->write_length);

This way you don't have to call i2c_{get,check}_functionality() repeatedly.

Thanks,
Guenter
	
>   		if (ret < 0)
>   			goto out;
>
>

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