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

[Alain Volmat]

Hi Jorge,

On Thu, Sep 08, 2022 at 10:36:22AM +0200, Jorge Ramirez-Ortiz, Foundries wrote:
> 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'm very sorry, it wasn't my intention at all but indeed I should have
taken more care to highlight your work.  Sorry about that.
I'm going to push a v2 for the serie, highlighting that and putting
your Signed-of first.

> 
> 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
> >