Re: [PATCH] i2c: complain loudly if __i2c_transfer has no proper callback

[Jean Delvare <jdelvare@suse.de>]

Hi Wolfram,

On Thu,  6 Jun 2024 22:36:58 +0200, Wolfram Sang wrote:
> In a discussion we concluded that having no working callback in
> __i2c_transfer is a serious bug, so dev_dbg() is not enough. Turn it
> into a WARN.
> 
> Link: https://lore.kernel.org/r/20240604171113.232628f9@endymion.delvare
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
>  drivers/i2c/i2c-core-base.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index db0d1ac82910..e5fd899c28c3 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2207,10 +2207,8 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  	unsigned long orig_jiffies;
>  	int ret, try;
>  
> -	if (!adap->algo->master_xfer) {
> -		dev_dbg(&adap->dev, "I2C level transfers not supported\n");
> +	if (WARN_ON_ONCE(!adap->algo->master_xfer))
>  		return -EOPNOTSUPP;
> -	}
>  
>  	if (WARN_ON(!msgs || num < 1))
>  		return -EINVAL;

Then you'll have to add a check on I2C_FUNC_I2C (or
adapter->algo->master_xfer, whatever you prefer) before calling
i2c_smbus_xfer_emulated(). Otherwise using i2c-dev on a slave-only
adapter will trigger the WARN_ON_ONCE immediately.

-- 
Jean Delvare
SUSE L3 Support