linux-kernel - Re: [PATCH 1/3] light sensor: Add SMBUS support to the tsl2563 driver.

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Date:	Wed, 22 Jun 2011 10:05:44 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	Bryan Freed <bfreed@...omium.org>
CC:	linux-kernel@...r.kernel.org, jbrenner@...sinc.com, gregkh@...e.de,
	arnd@...db.de,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Jean Delvare <khali@...ux-fr.org>,
	Amit Kucheria <amit.kucheria@...durent.com>
Subject: Re: [PATCH 1/3] light sensor: Add SMBUS support to the tsl2563 driver.

On 06/21/11 23:54, Bryan Freed wrote:
> This is so we can support it on x86 SMBUS adapters.
Hi Brian,

Please cc linux-iio@...r.kernel.org for iio patches.  Also this driver has fairly
clear authorship at the top, so more for your cc list. (added)
> 
> Signed-off-by: Bryan Freed <bfreed@...omium.org>
> ---
>  drivers/staging/iio/light/tsl2563.c |   29 ++++++++++++++++++++++++++++-
>  1 files changed, 28 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/staging/iio/light/tsl2563.c b/drivers/staging/iio/light/tsl2563.c
> index 9cffa2e..04aa155 100644
> --- a/drivers/staging/iio/light/tsl2563.c
> +++ b/drivers/staging/iio/light/tsl2563.c
> @@ -137,6 +137,8 @@ struct tsl2563_chip {
>  	u32			data1;
>  };
>  
> +static int use_smbus;
> +
>  static int tsl2563_write(struct i2c_client *client, u8 reg, u8 value)
>  {
>  	int ret;
> @@ -145,15 +147,35 @@ static int tsl2563_write(struct i2c_client *client, u8 reg, u8 value)
>  	buf[0] = TSL2563_CMD | reg;
>  	buf[1] = value;
>  
> +	if (use_smbus) {
> +		ret = i2c_smbus_write_byte_data(client, buf[0], value);
> +		return ret;
> +	}
> +
Here I'd prefer to see this in an else block to make the program flow clear. Same with the others.
Actually, is there any reason we can't use the smbus_write_byte_data for all cases?  I 'think'
it's emulated via i2c if that is available and smbus is not? (cc'd Jean to confirm this - though
a quick code browse of i2c-core.c looks promising.)

If smbus_xfer is not supplied by the adapter, i2c_smbus_xfer_emulated is called. 

The only possible issue I can think of is that a device supports full i2c + a partial smbus
support. (rather odd!)
>  	ret = i2c_master_send(client, buf, sizeof(buf));
>  	return (ret == sizeof(buf)) ? 0 : ret;
>  }
>  
> -static int tsl2563_read(struct i2c_client *client, u8 reg, void *buf, int len)
> +static int tsl2563_read(struct i2c_client *client, u8 reg, u8 *buf, int len)
>  {
>  	int ret;
>  	u8 cmd = TSL2563_CMD | reg;
>  
> +	if (use_smbus) {
> +		if (len == 1) {
> +			ret = i2c_smbus_read_byte_data(client, cmd);
> +			buf[0] = ret & 0xff;
> +		} else if (len == 2) {
> +			ret = i2c_smbus_read_word_data(client, cmd);
> +			buf[0] = ret & 0xff;
> +			buf[1] = (ret >> 8) & 0xff;
> +		} else
> +			ret = -1;
If we hit this something has gone hideously wrong.  Hence please
audit the driver to be sure this doesn't happen and don't bother
with this extra option.
> +		if (ret < 0)
> +			return 0; /* failure */
Please return the error, not 0 in event of failure.
> +		return len; /* success */
> +	}
> +
>  	ret = i2c_master_send(client, &cmd, sizeof(cmd));
>  	if (ret != sizeof(cmd))
>  		return ret;
> @@ -712,6 +734,11 @@ static int __devinit tsl2563_probe(struct i2c_client *client,
>  	int err = 0;
>  	int ret;
>  	u8 id;
> +	u32 smbus_func = I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA;
Can this be const?  Oddly, the answer looks to be no.  Given its an inline
in i2c.h, can't see why this one isn't const.  Jean, am I missing something
or wouldn't:
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index a6c652e..be5515d 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -458,7 +458,7 @@ static inline u32 i2c_get_functionality(struct i2c_adapter *adap)
 }
 
 /* Return 1 if adapter supports everything we need, 0 if not. */
-static inline int i2c_check_functionality(struct i2c_adapter *adap, u32 func)
+static inline int i2c_check_functionality(struct i2c_adapter *adap, const u32 func)
 {
        return (func & i2c_get_functionality(adap)) == func;
 }

Be a sensible change?  For that matter, this code should probably just have that
value inline in the function call as it isn't used anywhere else.

> +	/* We support both I2C and SMBUS adapter interfaces. */
> +	if (i2c_check_functionality(client->adapter, smbus_func))
> +		use_smbus = 1;
>  
>  	indio_dev = iio_allocate_device(sizeof(*chip));
>  	if (!indio_dev)

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