linux-kernel - Re: [PATCH] gpiolib: demote the hogging log messages to debug

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Date:   Tue, 13 Jun 2023 19:04:59 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: demote the hogging log messages to debug

On 6/12/23 10:42, Rob Herring wrote:
> On Sun, Jun 11, 2023 at 6:48 AM Frank Rowand <frowand.list@...il.com> wrote:
>>
>> On 6/11/23 07:39, Frank Rowand wrote:
>>> On 6/9/23 08:47, Rob Herring wrote:
>>>> On Mon, Jun 5, 2023 at 6:53 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>>>>>
>>>>> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>>>>
>>>>> Drivers should be silent when they work correctly. There's no reason to
>>>>> emit info messages when GPIO lines are hogged. Demote the message to
>>>>> debug.
>>>>>
>>>>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>>>> Suggested-by: Kent Gibson <warthog618@...il.com>
>>>>> ---
>>>>>  drivers/gpio/gpiolib.c |  2 +-
>>>>>  drivers/of/unittest.c  | 16 ++++++++--------
>>>>>  2 files changed, 9 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>>>>> index a7220e04a93e..e4515bda8915 100644
>>>>> --- a/drivers/gpio/gpiolib.c
>>>>> +++ b/drivers/gpio/gpiolib.c
>>>>> @@ -4243,7 +4243,7 @@ int gpiod_hog(struct gpio_desc *desc, const char *name,
>>>>>         /* Mark GPIO as hogged so it can be identified and removed later */
>>>>>         set_bit(FLAG_IS_HOGGED, &desc->flags);
>>>>>
>>>>> -       gpiod_info(desc, "hogged as %s%s\n",
>>>>> +       gpiod_dbg(desc, "hogged as %s%s\n",
>>>>>                 (dflags & GPIOD_FLAGS_BIT_DIR_OUT) ? "output" : "input",
>>>>>                 (dflags & GPIOD_FLAGS_BIT_DIR_OUT) ?
>>>>>                   (dflags & GPIOD_FLAGS_BIT_DIR_VAL) ? "/high" : "/low" : "");
>>>>> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
>>>>> index 2191c0136531..0060334a98a7 100644
>>>>> --- a/drivers/of/unittest.c
>>>>> +++ b/drivers/of/unittest.c
>>>>> @@ -1849,19 +1849,19 @@ static void __init of_unittest_overlay_gpio(void)
>>>>>          * driver is registered
>>>>>          */
>>>>>
>>>>> -       EXPECT_BEGIN(KERN_INFO,
>>>>> +       EXPECT_BEGIN(KERN_DEBUG,
>>>>>                      "gpio-<<int>> (line-B-input): hogged as input\n");
>>>>
>>>> As debug messages are normally off, I think you can just remove these.
>>>
>>> This patch is an example of exactly why the message level is the first parameter
>>> passed to EXPECT_*().  The test results are then _always_ valid, not just
>>> _normally_.
>>
>> One should never say never.  One should never say always. :-)
>>
>> Yes, there is still the exception where debug can be enabled independently
>> for drivers/gpio/gpiolib.c  vs for drivers/of/unittest.c.  And dynamic
>> debug can make things even more wonky.
> 
> If we turned on debug messages for drivers/of/, the unittest would be
> hopelessly broken.
> 
> Debug messages are special compared to all the other levels as they
> are normally off whereas the rest are always on. For the unittest we
> should assume they are off.

Sorry, I wasn't clear enough in my last email.  My intent in that email
is to essentially agree with what you say here - if debug is enabled
then we are in a special world where the person who enabled debug has
to deal with all of the side effects and consequences of enabling
debug.

-Frank

> 
> Rob