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

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Date:   Thu, 16 Apr 2020 20:35:56 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
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>,
        Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v1] iio: magnetometer: ak8974: Silence deferred-probe
 error

16.04.2020 19:51, Linus Walleij пишет:
> On Thu, Apr 16, 2020 at 4:45 PM Dmitry Osipenko <digetx@...il.com> wrote:
>> 16.04.2020 14:33, Linus Walleij пишет:
> 
>>> 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.
>>
>> Hello Linus,
>>
>> After some recent discussions in regards to the EPROBE_DEFER handling,
>> Thierry Reding suggested the form which is used in my patch and we
>> started to use it recently in the Tegra DRM driver [1]. The reason is
>> that we don't want to miss any deferred-probe messages under any
>> circumstances, for example like in a case of a disabled DYNAMIC_DEBUG.
> 
> I have a hard time to accept this reasoning.
> 
> Who doesn't feel that way about their subsystem? If you don't want
> to miss the message under any circumstances then use dev_info().
> Don't override the default behaviour of dev_dbg().
> 
>> The debug messages are usually disabled in a release-build and when not
>> a very experienced person hands you KMSG for diagnosing a problem, the
>> KMSG is pretty much useless if error is hidden silently.
> 
> So use dev_info().
> 
>> By moving the message to a debug level, we reduce the noise in the KMSG
>> because usually people look for a bold-red error messages. Secondly, we
>> don't introduce an additional overhead to the kernel size since the same
>> text is reused for all error conditions.
> 
> dev_info() is not supposed to be an error message, it is supposed to
> be information, so use that.

Okay, I'll make a v2. Thank you for the review.