linux-kernel - Re: [PATCH v1] iio: magnetometer: ak8974: Silence deferred-probe error

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Date:   Thu, 16 Apr 2020 13:33:03 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     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 v1] iio: magnetometer: ak8974: Silence deferred-probe error

Hi Dmitry,

thanks for your patch!

On Wed, Apr 15, 2020 at 12:27 AM Dmitry Osipenko <digetx@...il.com> wrote:

> It's not uncommon that voltage regulator becomes available later during
> kernel's boot process, in this case there is no need to print a noisy
> error message. This patch moves the message about unavailable regulator
> to the debug level in a case of the deferred-probe error and also amends
> the message with error code.
>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/iio/magnetometer/ak8974.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iio/magnetometer/ak8974.c b/drivers/iio/magnetometer/ak8974.c
> index d32996702110..cc3861f97d42 100644
> --- a/drivers/iio/magnetometer/ak8974.c
> +++ b/drivers/iio/magnetometer/ak8974.c
> @@ -718,6 +718,7 @@ static const struct regmap_config ak8974_regmap_config = {
>  static int ak8974_probe(struct i2c_client *i2c,
>                         const struct i2c_device_id *id)
>  {
> +       const char *level = KERN_ERR;
>         struct iio_dev *indio_dev;
>         struct ak8974 *ak8974;
>         unsigned long irq_trig;
> @@ -746,7 +747,11 @@ static int ak8974_probe(struct i2c_client *i2c,
>                                       ARRAY_SIZE(ak8974->regs),
>                                       ak8974->regs);
>         if (ret < 0) {
> -               dev_err(&i2c->dev, "cannot get regulators\n");
> +               if (ret == -EPROBE_DEFER)
> +                       level = KERN_DEBUG;
> +
> +               dev_printk(level, &i2c->dev, "cannot get regulators: %d\n",

This misses some important aspects of dev_dbg(), notably this:

#if defined(CONFIG_DYNAMIC_DEBUG)
#define dev_dbg(dev, fmt, ...)                                          \
        dynamic_dev_dbg(dev, dev_fmt(fmt), ##__VA_ARGS__)
#elif defined(DEBUG)
#define dev_dbg(dev, fmt, ...)                                          \
        dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__)
#else
#define dev_dbg(dev, fmt, ...)                                          \
({                                                                      \
        if (0)                                                          \
                dev_printk(KERN_DEBUG, dev, dev_fmt(fmt), ##__VA_ARGS__); \
})
#endif

If DEBUG is not defined the entire dev_dbg() message is enclodes in if (0)
and compiled out of the kernel, saving space. The above does not
fulfil that.

Yours,
Linus Walleij