linux-kernel - Re: [PATCH 1/3] driver core: add probe

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Message-Id: <20181016125543eucas1p1f23b3482179a9cd465f509e0abf782c1~eGAecmAv93038330383eucas1p1j@eucas1p1.samsung.com>
Date:   Tue, 16 Oct 2018 14:55:41 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Javier Martinez Canillas <javierm@...hat.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 1/3] driver core: add probe_err log helper

On 16.10.2018 13:29, Andrzej Hajda wrote:
> On 16.10.2018 13:01, Andy Shevchenko wrote:
>> On Tue, Oct 16, 2018 at 10:22 AM Andrzej Hajda <a.hajda@...sung.com> wrote:
>>> During probe every time driver gets resource it should usually check for error
>>> printk some message if it is not -EPROBE_DEFER and return the error. This
>>> pattern is simple but requires adding few lines after any resource acquisition
>>> code, as a result it is often omited or implemented only partially.
>>> probe_err helps to replace such code seqences with simple call, so code:
>>>         if (err != -EPROBE_DEFER)
>>>                 dev_err(dev, ...);
>>>         return err;
>>> becomes:
>>>         return probe_err(dev, err, ...);
>>>
>>> Signed-off-by: Andrzej Hajda <a.hajda@...sung.com>
>>> ---
>>>  drivers/base/core.c    | 37 +++++++++++++++++++++++++++++++++++++
>>>  include/linux/device.h |  2 ++
>>>  2 files changed, 39 insertions(+)
>>>
>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>> index 04bbcd779e11..23fabefb217a 100644
>>> --- a/drivers/base/core.c
>>> +++ b/drivers/base/core.c
>>> @@ -3067,6 +3067,43 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>>>
>>>  #endif
>>>
>>> +/**
>>> + * probe_err - probe error check and log helper
>>> + * @dev: the pointer to the struct device
>>> + * @err: error value to test
>>> + * @fmt: printf-style format string
>>> + * @...: arguments as specified in the format string
>>> + *
>>> + * This helper implements common pattern present in probe functions for error
>>> + * checking: print message if the error is not -EPROBE_DEFER and propagate it.
>>> + * It replaces code sequence:
>>> + *     if (err != -EPROBE_DEFER)
>>> + *             dev_err(dev, ...);
>>> + *     return err;
>>> + * with
>>> + *     return probe_err(dev, err, ...);
>>> + *
>>> + * Returns @err.
>>> + *
>>> + */
>>> +int probe_err(const struct device *dev, int err, const char *fmt, ...)
>>> +{
>>> +       struct va_format vaf;
>>> +       va_list args;
>>> +
>>> +       if (err != -EPROBE_DEFER) {
>> Why not
>>
>> if (err == ...)
>>  return err;
>>
>> ...
>> return err;
>>
>> ?
>>
>> Better to read, better to maintain. No?
> Yes, anyway next patch will re-factor it anyway.
>
>>> +               va_start(args, fmt);
>>> +
>>> +               vaf.fmt = fmt;
>>> +               vaf.va = &args;
>>> +
>>> +               __dev_printk(KERN_ERR, dev, &vaf);
>> It would be nice to print an error code as well, wouldn't it?
> Hmm, on probe fail error is printed anyway (with exception of
> EPROBE_DEFER, ENODEV and ENXIO):
>     "probe of %s failed with error %d\n"
> On the other side currently some drivers prints the error code anyway
> via dev_err or similar, so I guess during conversion to probe_err it
> should be removed then.
>
> If we add error code to probe_err is it OK to report it this way?
>     dev_err(dev, "%V, %d\n", &vaf, err);

Ups, I forgot that message passed to probe_err will contain already
newline character.
So the err must be before message passed to probe_err, for example:
    dev_err(dev, "err=%d: %V\n", err, &vaf);
Is it OK? Or better leave this part of the patch as is?

Regards
Andrzej

>
> Regards
> Andrzej
>
>>> +               va_end(args);
>>> +       }
>>> +
>>> +       return err;
>>> +}
>>> +
>>>  static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
>>>  {
>>>         return fwnode && !IS_ERR(fwnode->secondary);
>>> diff --git a/include/linux/device.h b/include/linux/device.h
>>> index 90224e75ade4..06c2c797d132 100644
>>> --- a/include/linux/device.h
>>> +++ b/include/linux/device.h
>>> @@ -1577,6 +1577,8 @@ do {                                                                      \
>>>         WARN_ONCE(condition, "%s %s: " format, \
>>>                         dev_driver_string(dev), dev_name(dev), ## arg)
>>>
>>> +int probe_err(const struct device *dev, int err, const char *fmt, ...);
>>> +
>>>  /* Create alias, so I can be autoloaded. */
>>>  #define MODULE_ALIAS_CHARDEV(major,minor) \
>>>         MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
>>> --
>>> 2.18.0
>>>