[PATCH 3/3] i2c: stm32: only send a STOP upon transfer completion

[Jorge Ramirez-Ortiz, Foundries]

On 08/09/22, Alain Volmat wrote:
> Current function stm32_i2c_message_xfer is sending a STOP
> whatever the result of the transaction is.  This can cause issues
> such as making the bus busy since the controller itself is already
> sending automatically a STOP when a NACK is generated.  This can
> be especially seen when the processing get slower (ex: enabling lots
> of debug messages), ending up send 2 STOP (one automatically by the
> controller and a 2nd one at the end of the stm32_i2c_message_xfer
> function).

um I debugged this - took me a couple of days - and I proposed a fix that has just
been massaged a little in this PR.

IMO the best thing to do is either adding me - or to be fair yourself since you
invested almost zero time on it - as a co-author. The hard bit was to find the
issue in the first place.

what do you think?

I'll try to find some time to test this.

> 
> Signed-off-by: Alain Volmat <alain.volmat at foss.st.com>
> ---
>  drivers/i2c/stm32f7_i2c.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/stm32f7_i2c.c b/drivers/i2c/stm32f7_i2c.c
> index 0ec67b5c12..8803979d3e 100644
> --- a/drivers/i2c/stm32f7_i2c.c
> +++ b/drivers/i2c/stm32f7_i2c.c
> @@ -477,16 +477,16 @@ static int stm32_i2c_message_xfer(struct stm32_i2c_priv *i2c_priv,
>  			if (ret)
>  				break;
>  
> +			/* End of transfer, send stop condition */
> +			mask = STM32_I2C_CR2_STOP;
> +			setbits_le32(&regs->cr2, mask);
> +
>  			if (!stop)
>  				/* Message sent, new message has to be sent */
>  				return 0;
>  		}
>  	}
>  
> -	/* End of transfer, send stop condition */
> -	mask = STM32_I2C_CR2_STOP;
> -	setbits_le32(&regs->cr2, mask);
> -
>  	return stm32_i2c_check_end_of_message(i2c_priv);
>  }
>  
> -- 
> 2.25.1
>