linux-kernel - Re: [PATCH v2 3/3] i2c: rk3x: Add check for clk

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Message-ID: <CAD=FV=VzqKa=fo4KRw4FSpPcH4mVnt8jBMo=FMzsGkdGrXCfxg@mail.gmail.com>
Date: Tue, 5 Nov 2024 13:29:40 -0800
From: Doug Anderson <dianders@...omium.org>
To: Jiasheng Jiang <jiashengjiangcool@...il.com>
Cc: andi.shyti@...nel.org, rmk@...-67.arm.linux.org.uk, max.schwarz@...ine.de, 
	david.wu@...k-chips.com, heiko@...ech.de, vz@...ia.com, wsa@...nel.org, 
	manabian@...il.com, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-i2c@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] i2c: rk3x: Add check for clk_enable()

Hi,

On Tue, Nov 5, 2024 at 8:18 AM Jiasheng Jiang
<jiashengjiangcool@...il.com> wrote:
>
> Add check for the return value of clk_enable() in order to catch the
> potential exception. Moreover, convert the return type of
> rk3x_i2c_adapt_div() into int and add the check.
>
> Signed-off-by: Jiasheng Jiang <jiashengjiangcool@...il.com>
> ---
> Changelog:
>
> v1 -> v2:
>
> 1. Remove the Fixes tag.
> 2. Use dev_err_probe to simplify error handling.
> ---
>  drivers/i2c/busses/i2c-rk3x.c | 51 +++++++++++++++++++++++++----------
>  1 file changed, 37 insertions(+), 14 deletions(-)

Wow, this is a whole lot of code to add to check for an error that
can't really happen as far as I'm aware. Turning on a clock is just
some MMIO writes and can't fail, right? Is this really worth it? Maybe
just wrap clk_enable() and spam an error to the logs if it fails? If
we ever see that error we can figure out what's going on and if
there's a sensible reason it could fail we could add the more complex
code.


> @@ -883,7 +883,9 @@ static void rk3x_i2c_adapt_div(struct rk3x_i2c *i2c, unsigned long clk_rate)
>         ret = i2c->soc_data->calc_timings(clk_rate, t, &calc);
>         WARN_ONCE(ret != 0, "Could not reach SCL freq %u", t->bus_freq_hz);
>
> -       clk_enable(i2c->pclk);
> +       ret = clk_enable(i2c->pclk);
> +       if (ret)
> +               return dev_err_probe(i2c->dev, ret, "Can't enable bus clk for rk3399: %d\n", ret);

Officially you're only supposed to use "dev_err_probe()" from probe or
calls indirectly called from probe. You're now using it in a whole lot
of other places.

...also note that dev_err_probe() already prints the error so you
don't need to include it in your error message.


> @@ -942,19 +946,27 @@ static int rk3x_i2c_clk_notifier_cb(struct notifier_block *nb, unsigned long
>                         return NOTIFY_STOP;
>
>                 /* scale up */
> -               if (ndata->new_rate > ndata->old_rate)
> -                       rk3x_i2c_adapt_div(i2c, ndata->new_rate);
> +               if (ndata->new_rate > ndata->old_rate) {
> +                       if (rk3x_i2c_adapt_div(i2c, ndata->new_rate))
> +                               return NOTIFY_STOP;
> +               }
>
>                 return NOTIFY_OK;
>         case POST_RATE_CHANGE:
>                 /* scale down */
> -               if (ndata->new_rate < ndata->old_rate)
> -                       rk3x_i2c_adapt_div(i2c, ndata->new_rate);
> +               if (ndata->new_rate < ndata->old_rate) {
> +                       if (rk3x_i2c_adapt_div(i2c, ndata->new_rate))
> +                               return NOTIFY_STOP;
> +               }
> +
>                 return NOTIFY_OK;
>         case ABORT_RATE_CHANGE:
>                 /* scale up */
> -               if (ndata->new_rate > ndata->old_rate)
> -                       rk3x_i2c_adapt_div(i2c, ndata->old_rate);
> +               if (ndata->new_rate > ndata->old_rate) {
> +                       if (rk3x_i2c_adapt_div(i2c, ndata->old_rate))
> +                               return NOTIFY_STOP;

I'm not convinced you can actually return NODIFY_STOP from the
POST_RATE_CHANGE or ABORT_RATE_CHANGE. Have you confirmed that is
actually sensible?


> @@ -1365,9 +1385,12 @@ static int rk3x_i2c_probe(struct platform_device *pdev)
>         }
>
>         clk_rate = clk_get_rate(i2c->clk);
> -       rk3x_i2c_adapt_div(i2c, clk_rate);
> +       ret = rk3x_i2c_adapt_div(i2c, clk_rate);
>         clk_disable(i2c->clk);
>
> +       if (ret)
> +               goto err_clk_notifier;

This one seems especially comical to add since the only way
rk3x_i2c_adapt_div() could fail would be if a nested clk_enable()
failed. ...and I'm 99% sure that's not possible.

-Doug