Re: [PATCH] regmap: Fix i2c word access when using SMBus access functions

[Jean Delvare <jdelvare@suse.de>]

Hi Guenter,

On Sun,  1 Feb 2015 15:48:01 -0800, Guenter Roeck wrote:
> SMBUs access functions assume that 16 bit values are formatted as

Correct spelling is SMBus (lowercase U.) Also I think "16 bit" is
better spelled "16-bit" (more occurrences below.)

> little endian numbers. The direct i2c access functions in regmap,
> however, assume that 16 bit values are formatted as big endian numbers.
> As a result, the current code returns different values if an i2c chip's
> 16 bit registers are accessed through i2c access functions vs. SMBus
> access functions.
> 
> Use regmap_smbus_read_word_swapped and regmap_smbus_write_word_swapped
> for 16 bit SMBus accesses unless a chip is registered with val_format_endian
> set to REGMAP_ENDIAN_LITTLE. In the latter case, keep using
> regmap_smbus_write_word_data and regmap_smbus_read_word_data.
> 
> Cc: Jean Delvare <jdelvare@suse.de>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> Might be a candidate for -stable, though as far as I can see there is currently
> no driver in the upstream kernel using regmap for 16-bit i2c accesses.
> 
>  drivers/base/regmap/regmap-i2c.c | 41 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c
> index 053150a..865f4f8 100644
> --- a/drivers/base/regmap/regmap-i2c.c
> +++ b/drivers/base/regmap/regmap-i2c.c
> @@ -87,6 +87,42 @@ static struct regmap_bus regmap_smbus_word = {
>  	.reg_read = regmap_smbus_word_reg_read,
>  };
>  
> +static int regmap_smbus_word_read_swapped(void *context, unsigned int reg,
> +					  unsigned int *val)
> +{
> +	struct device *dev = context;
> +	struct i2c_client *i2c = to_i2c_client(dev);
> +	int ret;
> +
> +	if (reg > 0xff)
> +		return -EINVAL;
> +
> +	ret = i2c_smbus_read_word_swapped(i2c, reg);
> +	if (ret < 0)
> +		return ret;
> +
> +	*val = ret;
> +
> +	return 0;
> +}
> +
> +static int regmap_smbus_word_write_swapped(void *context, unsigned int reg,
> +					   unsigned int val)
> +{
> +	struct device *dev = context;
> +	struct i2c_client *i2c = to_i2c_client(dev);
> +
> +	if (val > 0xffff || reg > 0xff)
> +		return -EINVAL;
> +
> +	return i2c_smbus_write_word_swapped(i2c, reg, val);
> +}
> +
> +static struct regmap_bus regmap_smbus_word_swapped = {
> +	.reg_write = regmap_smbus_word_write_swapped,
> +	.reg_read = regmap_smbus_word_read_swapped,
> +};
> +
>  static int regmap_i2c_write(void *context, const void *data, size_t count)
>  {
>  	struct device *dev = context;
> @@ -180,7 +216,10 @@ static const struct regmap_bus *regmap_get_i2c_bus(struct i2c_client *i2c,
>  	else if (config->val_bits == 16 && config->reg_bits == 8 &&
>  		 i2c_check_functionality(i2c->adapter,
>  					 I2C_FUNC_SMBUS_WORD_DATA))
> -		return &regmap_smbus_word;
> +			if (config->val_format_endian == REGMAP_ENDIAN_LITTLE)
> +				return &regmap_smbus_word;
> +			else
> +				return &regmap_smbus_word_swapped;

Indentation looks wrong.

>  	else if (config->val_bits == 8 && config->reg_bits == 8 &&
>  		 i2c_check_functionality(i2c->adapter,
>  					 I2C_FUNC_SMBUS_BYTE_DATA))

The code itself looks sane, although I am not a regmap expert.

Reviewed-by: Jean Delvare <jdelvare@suse.de>

-- 
Jean Delvare
SUSE L3 Support