linux-kernel - Re: [PATCH] iio: magnetometer: ak8974: Fix runtime PM imbalance on error

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Date:   Mon, 25 May 2020 14:08:25 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     Kangjie Lu <kjlu@....edu>, Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: magnetometer: ak8974: Fix runtime PM imbalance on error

On Sun, May 24, 2020 at 4:51 AM Dinghao Liu <dinghao.liu@....edu.cn> wrote:

> When devm_regmap_init_i2c() returns an error code, a pairing
> runtime PM usage counter decrement is needed to keep the
> counter balanced. For error paths after ak8974_set_power(),
> ak8974_detect() and ak8974_reset(), things are the same.
>
> However, When iio_triggered_buffer_setup() returns an error
> code, we don't need such a decrement because there is already
> one before this call. Things are the same for other error paths
> after it.
>
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>

>         ak8974->map = devm_regmap_init_i2c(i2c, &ak8974_regmap_config);
>         if (IS_ERR(ak8974->map)) {
>                 dev_err(&i2c->dev, "failed to allocate register map\n");
> +               pm_runtime_put_noidle(&i2c->dev);
> +               pm_runtime_disable(&i2c->dev);
>                 return PTR_ERR(ak8974->map);

This is correct.

>         ret = ak8974_set_power(ak8974, AK8974_PWR_ON);
>         if (ret) {
>                 dev_err(&i2c->dev, "could not power on\n");
> +               pm_runtime_put_noidle(&i2c->dev);
> +               pm_runtime_disable(&i2c->dev);
>                 goto power_off;

What about just changing this to goto disable_pm;

>         ret = ak8974_detect(ak8974);
>         if (ret) {
>                 dev_err(&i2c->dev, "neither AK8974 nor AMI30x found\n");
> +               pm_runtime_put_noidle(&i2c->dev);
> +               pm_runtime_disable(&i2c->dev);
>                 goto power_off;

goto disable_pm;

> @@ -786,6 +792,8 @@ static int ak8974_probe(struct i2c_client *i2c,
>         ret = ak8974_reset(ak8974);
>         if (ret) {
>                 dev_err(&i2c->dev, "AK8974 reset failed\n");
> +               pm_runtime_put_noidle(&i2c->dev);
> +               pm_runtime_disable(&i2c->dev);

goto disable_pm;

>  disable_pm:
> -       pm_runtime_put_noidle(&i2c->dev);
>         pm_runtime_disable(&i2c->dev);
>         ak8974_set_power(ak8974, AK8974_PWR_OFF);

Keep the top pm_runtime_put_noidle().

The ak8974_set_power() call is fine, the power on call does not
need to happen in balance. Sure it will attempt to write a register
but so will the power on call.

Yours,
Linus Walleij