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

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Date:   Tue, 16 Oct 2018 13:29:48 +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 13:01, 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);

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
>>
>