linux-kernel - Re: [PATCH v7 2/5] i2c: core: run atomic i2c xfer when !preemptible

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Date:   Tue, 14 Nov 2023 12:43:37 -0600
From:   Chris Morgan <macroalpha82@...il.com>
To:     Benjamin Bara <bbara93@...il.com>
Cc:     benjamin.bara@...data.com, dmitry.osipenko@...labora.com,
        heiko@...ech.de, jonathanh@...dia.com, lee@...nel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, max.schwarz@...ine.de, nm@...com,
        peterz@...radead.org, rafael.j.wysocki@...el.com,
        richard.leitner@...ux.dev, stable@...r.kernel.org,
        treding@...dia.com, wsa+renesas@...g-engineering.com,
        wsa@...nel.org
Subject: Re: [PATCH v7 2/5] i2c: core: run atomic i2c xfer when !preemptible

On Mon, Nov 13, 2023 at 04:48:26PM +0100, Benjamin Bara wrote:
> Hi!
> 
> Thanks for testing and the feedback!
> 
> On Mon, 13 Nov 2023 at 15:54, Chris Morgan <macroalpha82@...il.com> wrote:
> > I can confirm I no longer get any of the errors with this patch. Tested
> > on both an Anbernic RG353P (RK3566 with an RK817 PMIC) and an Odroid
> > Go Advance (RK3326 with an RK817 PMIC). The device appears to shut
> > down consistently again and I no longer see these messages in my dmesg
> > log when I shut down.
> 
> Just to make sure: Are you compiling with CONFIG_PREEMPTION (and
> therefore CONFIG_PREEMPT_COUNT)?
> 
> If yes, could you please also test the following patch? Because I am not
> sure yet how polling can be false in a "polling required" situation,
> meaning .master_xfer() is called instead of .master_xfer_atomic() (while
> your test shows that irq_disabled() is true, which is basically done
> with !preemptible()). The patch should test the other way round: if the
> situation is found, force an atomic transfer instead.
> 
> Thank you!
> 
> diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> index a044ca0c35a1..6e3e8433018f 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -1131,6 +1131,10 @@ static int rk3x_i2c_xfer_common(struct i2c_adapter *adap,
>  static int rk3x_i2c_xfer(struct i2c_adapter *adap,
>                          struct i2c_msg *msgs, int num)
>  {
> +       if (irqs_disabled()) {
> +               WARN_ONCE(1, "Landed in non-atomic handler with disabled IRQs");
> +               return rk3x_i2c_xfer_common(adap, msgs, num, true);
> +       }
>         return rk3x_i2c_xfer_common(adap, msgs, num, false);
>  }
> 

I have CONFIG_PREEMPT_VOLUNTARY=y but CONFIG_PREEMPTION is not set.

Thank you.