linux-kernel - Re: [PATCH v4 9/9] i2c: riic: Add `riic_bus

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Message-ID: <CA+V-a8sq918O+iwxNnfG2g6JPrWyCvpetzD149u48_Scbbct6A@mail.gmail.com>
Date: Fri, 3 Jan 2025 16:12:48 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Chris Brandt <chris.brandt@...esas.com>, Andi Shyti <andi.shyti@...nel.org>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	Andy Shevchenko <andy.shevchenko@...il.com>, Philipp Zabel <p.zabel@...gutronix.de>, 
	linux-renesas-soc@...r.kernel.org, linux-i2c@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v4 9/9] i2c: riic: Add `riic_bus_barrier()` to check bus availability

Hi Geert,

On Fri, Jan 3, 2025 at 4:09 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Fri, Jan 3, 2025 at 10:19 AM Prabhakar <prabhakar.csengg@...il.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...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@...renesas.com>
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> > Tested-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> > Tested-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> > Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@...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@...ux-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