Re: [PATCH] i2c: ocores: generate stop condition after timeout in polling mode

[Federico Vaga]

On Wed, Apr 12, 2023 at 11:49:32AM +0200, Matthias Schiffer wrote:
> On Mon, 2023-02-20 at 16:17 +0000, Matthias Schiffer wrote:
> > From: Gregor Herburger <gregor.herburger@xxxxxxxxxxxx>
> >
> > In polling mode, no stop condition is generated after a timeout. This
> > causes SCL to remain low and thereby block the bus. If this happens
> > during a transfer it can cause slaves to misinterpret the subsequent
> > transfer and return wrong values.
> >
> > To solve this, pass the ETIMEDOUT error up from ocores_process_polling()
> > instead of setting STATE_ERROR directly. The caller is adjusted to call
> > ocores_process_timeout() on error both in polling and in IRQ mode, which
> > will set STATE_ERROR and generate a stop condition.

I can see and confirm the bug.

The patch seems fine to me, but I do not have the hardware at hand right now for a
real test.

Following a few cosmetic comments.

> > Fixes: 69c8c0c0efa8 ("i2c: ocores: add polling interface")
> > Signed-off-by: Gregor Herburger <gregor.herburger@xxxxxxxxxxxx>
> > Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
>
>
> Any chance we can get someone to have a look at this patch?
>
> Regards,
> Matthias
>
>
>
> > ---
> >  drivers/i2c/busses/i2c-ocores.c | 28 +++++++++++++++-------------
> >  1 file changed, 15 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
> > index a0af027db04c1..28bcda3f7040a 100644
> > --- a/drivers/i2c/busses/i2c-ocores.c
> > +++ b/drivers/i2c/busses/i2c-ocores.c
> > @@ -342,18 +342,18 @@ static int ocores_poll_wait(struct ocores_i2c *i2c)
> >   * ocores_isr(), we just add our polling code around it.
> >   *
> >   * It can run in atomic context
> > + *
> > + * Return: 0 on success, -ETIMEDOUT on timeout
> >   */
> > -static void ocores_process_polling(struct ocores_i2c *i2c)
> > +static int ocores_process_polling(struct ocores_i2c *i2c)
> >  {
> >  	while (1) {
> >  		irqreturn_t ret;
> >  		int err;
> >
> >  		err = ocores_poll_wait(i2c);
> > -		if (err) {
> > -			i2c->state = STATE_ERROR;
> > -			break; /* timeout */
> > -		}
> > +		if (err)
> > +			return err;
> >
> >  		ret = ocores_isr(-1, i2c);
> >  		if (ret == IRQ_NONE)
> > @@ -364,6 +364,8 @@ static void ocores_process_polling(struct ocores_i2c *i2c)
> >  					break;
> >  		}
> >  	}
> > +
> > +	return 0;
> >  }

I would try to have a single return point at the end `return err` and inside the
loop just a break.

> >  static int ocores_xfer_core(struct ocores_i2c *i2c,
> > @@ -387,16 +389,16 @@ static int ocores_xfer_core(struct ocores_i2c *i2c,
> >  	oc_setreg(i2c, OCI2C_DATA, i2c_8bit_addr_from_msg(i2c->msg));
> >  	oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
> >
> > -	if (polling) {
> > -		ocores_process_polling(i2c);
> > -	} else {
> > +	if (polling)
> > +		ret = ocores_process_polling(i2c);
> > +	else
> >  		ret = wait_event_timeout(i2c->wait,
> >  					 (i2c->state == STATE_ERROR) ||
> > -					 (i2c->state == STATE_DONE), HZ);
> > -		if (ret == 0) {
> > -			ocores_process_timeout(i2c);
> > -			return -ETIMEDOUT;
> > -		}
> > +					 (i2c->state == STATE_DONE), HZ) ?
> > +						0 : -ETIMEDOUT;

For readability, I would avoid the ternary operator here and do the assignement
with an `if` as it was before.

if (ret == 0)
    ret = -ETIMEDOUT;

> > +	if (ret) {
> > +		ocores_process_timeout(i2c);
> > +		return ret;
> >  	}
> >
> >  	return (i2c->state == STATE_DONE) ? num : -EIO;
>
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--
Federico Vaga - CERN BE-CEM-EDL