Re: [PATCH v4 9/9] i2c: riic: Add `riic_bus_barrier()` to check bus availability

Lad, Prabhakar
2025-01-03T16:13:16Z

Hi Geert,

On Fri, Jan 3, 2025 at 4:09 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Fri, Jan 3, 2025 at 10:19 AM Prabhakar <prabhakar.csengg@gmail.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> >
> > Introduce a new `riic_bus_barrier()` function to verify bus availability
> > before initiating an I2C transfer. This function enhances the bus
> > arbitration check by ensuring that the SDA and SCL lines are not held low,
> > in addition to checking the BBSY flag using `readb_poll_timeout()`.
> >
> > Previously, only the BBSY flag was checked to determine bus availability.
> > However, it is possible for the SDA line to remain low even when BBSY = 0.
> > This new implementation performs an additional check on the SDA and SCL
> > lines to avoid potential bus contention issues.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> > Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> > Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> > Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> > ---
> > v3->v4
> > - Propogated error code when readb_poll_timeout() failed
> > - I've kept the RB/TB tags as the changes were minimal.
>
> OK.
>
> + you removed a superfluous initialization of riic->err (last change below).
>
This change was requested by Wolfram on v2.

[0] https://lore.kernel.org/all/Z2XhI4L9nzUqa22Z@ninjato/

Cheers,
Prabhakar

> > --- a/drivers/i2c/busses/i2c-riic.c
> > +++ b/drivers/i2c/busses/i2c-riic.c
> > @@ -149,13 +173,11 @@ static int riic_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> > if (ret)
> > return ret;
> >
> > - if (riic_readb(riic, RIIC_ICCR2) & ICCR2_BBSY) {
> > - riic->err = -EBUSY;
> > + riic->err = riic_bus_barrier(riic);
> > + if (riic->err)
> > goto out;
> > - }
> >
> > reinit_completion(&riic->msg_done);
> > - riic->err = 0;
> >
> > riic_writeb(riic, 0, RIIC_ICSR2);
> >
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds