netdev - Re: [PATCH net-next] mdio_bus: Remove unneeded gpiod NULL check

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Date:   Fri, 8 Sep 2017 12:56:50 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Woojung.Huh@...rochip.com, linus.walleij@...aro.org
Cc:     andrew@...n.ch, festevam@...il.com,
        sergei.shtylyov@...entembedded.com, davem@...emloft.net,
        netdev@...r.kernel.org, fabio.estevam@....com
Subject: Re: [PATCH net-next] mdio_bus: Remove unneeded gpiod NULL check

On 09/07/2017 02:51 PM, Woojung.Huh@...rochip.com wrote:
>>>>> If someone is using GPIO descriptors with GPIO disabled, i.e. calling
>>>>> gpiod_get() and friends, this is very likely to be a bug, and what
>>>>> the driver wants to do is:
>>>>>
>>>>>  depends on GPIOLIB
>>>>>
>>>>> or
>>>>>
>>>>>  select GPIOLIB
>>>>>
>>>>> in Kconfig. The whole optional thing is mainly a leftover from when it
>>>>> was possible to have a local implementation of the GPIOLIB API in
>>>>> some custom header file, noone sane should be doing that anymore,
>>>>> and if they do, they can very well face the warnings.
>>>>>
>>>>> If someone is facing a lot of WARN_ON() messages to this, it is a clear
>>>>> indication that they need to fix their Kconfig and in that case it is proper.
>>>> Linus & Andrew,
>>>>
>>>> I knew that it is already in David's pulling request.
>>>> Configuring GPIOLIB is the right solution  even if platform doesn't use it?
>>>
>>> I guess?
>>>
>>> "Platform doesn't use it" what does that mean?
>>>
>>> Does it mean it does not call the
>>> APIs of the GPIOLIB, does it mean it doesn't have a GPIO driver
>>> at probe (but may have one by having it probed from a module)
>>> or does it mean the platform can never have it?
>>
>> I think it means CONFIG_GPIOLIB=n in the kernel because it's not needed,
>> yet you run code (like drivers/net/phy/mdio_bus.c) that unconditionally
>> calls into GPIOLIB and attempts to configure a given GPIO if available.
> Yes. I'm facing issue on PC which won't need GPIOLIB as default.
> Warning message goes away when GPIOLIB is enabled, and fortunately,
> Ubuntu default config has it.
> So, it may not be seen by many users when with full/default configuration.

Woojung, I suppose you are also getting a warning from
gpiod_set_value_cansleep() done in mdiobus_unregister() right? With
CONFIG_GPIOLIB=n devm_gpiod_get_optional() returns NULL, which we don't
check as an error, on purpose however we still call
gpiod_set_value_cansleep() on a NULL GPIO descriptor, so the following
should do:

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index b6f9fa670168..67dbb7c26840 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -424,7 +424,8 @@ void mdiobus_unregister(struct mii_bus *bus)
        }

        /* Put PHYs in RESET to save power */
-       gpiod_set_value_cansleep(bus->reset_gpiod, 1);
+       if (!IS_ERR_OR_NULL(bus->reset_gpiod))
+               gpiod_set_value_cansleep(bus->reset_gpiod, 1);

        device_del(&bus->dev);
 }


> 
>> This thread is actually what prompted me to write this email:
>>
>> https://lkml.org/lkml/2017/9/2/3
> Thanks for the link.
> 
> 


-- 
Florian