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

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Message-ID: <CAMuHMdV-1j0aN9Ko3oUnRZ363wiy84ZVDoV4ZsS4xTLn+u3tKw@mail.gmail.com>
Date: Fri, 3 Jan 2025 17:09:00 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Prabhakar <prabhakar.csengg@...il.com>
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 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).

> --- 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