[PATCH v2 3/3] i2c: stm32: only send a STOP upon transfer completion

[Patrick DELAUNAY]

Hi,

On 9/8/22 12:59, 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).
>
> Thanks to Jorge Ramirez-Ortiz for diagnosing and proposing a first
> fix for this. [1]
>
> [1] https://lore.kernel.org/u-boot/20220815145211.31342-2-jorge@foundries.io/
>
> Reported-by: Jorge Ramirez-Ortiz, Foundries <jorge at foundries.io>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge at foundries.io>
> 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);
>   }
>   


Reviewed-by: Patrick Delaunay <patrick.delaunay at foss.st.com>

Thanks
Patrick