16.04.2020 14:33, Linus Walleij пишет:
> Hi Dmitry,
>
> thanks for your patch!
>
> On Wed, Apr 15, 2020 at 12:27 AM Dmitry Osipenko <digetx@xxxxxxxxx> 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@xxxxxxxxx>
>> ---
>> 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.
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.
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.
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.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e32c8c2a5fbe1514e4ae9063a49e76ecf486ffb8
I can change this patch to something like this:
if (ret == -EPROBE_DEFER)
dev_dbg("deferring probe\n");
else
dev_err("cannot...");
but in general this should be a less useful variant, don't you agree?
