linux-kernel - Re: [PATCH 3/5] gpio: of: Return error if gpio hog configuration failed

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Date:	Thu, 10 Mar 2016 12:32:22 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	<linus.walleij@...aro.org>, <robh+dt@...nel.org>,
	<pawel.moll@....com>, <mark.rutland@....com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-gpio@...r.kernel.org>, <treding@...dia.com>,
	Benoit Parrot <bparrot@...com>,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH 3/5] gpio: of: Return error if gpio hog configuration
 failed


On Wednesday 09 March 2016 10:41 PM, Stephen Warren wrote:
> On 03/08/2016 05:02 AM, Laxman Dewangan wrote:
>> If GPIO hog configuration failed while adding OF based
>> gpiochip() then return the error instead of ignoring it.
>>
>> This helps of properly handling the gpio driver dependency.
>>
>> When adding the gpio hog nodes for NVIDIA's Tegra210 platforms,
>> the gpio_hogd() fails with EPROBE_DEFER because pinctrl is not
>> ready at this time and gpio_request() for Tegra GPIO driver
>> returns error. The error was not causing the Tegra GPIO driver
>> to fail as the error was getting ignored.
>
>> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
>
>> @@ -218,9 +220,12 @@ static void of_gpiochip_scan_gpios(struct 
>> gpio_chip *chip)
>>           if (IS_ERR(desc))
>>               continue;
>>
>> -        if (gpiod_hog(desc, name, lflags, dflags))
>> -            continue;
>> +        ret = gpiod_hog(desc, name, lflags, dflags);
>> +        if (ret < 0)
>> +            return ret;
>>       }
>> +
>> +    return 0;
>>   }
>
> If there are multiple child nodes (which the code above is looping 
> over), and the hog for entries 0, 1, 2 succeed and the hog for entry 3 
> fails, don't you need to go back and unhog for nodes 0..2 so that the 
> next time this function is called, those hogs won't already be in 
> place thus preventing them from being hogged the second time around? 
> Or does hogging not take ownership of the resource and thus prevent it 
> from being acquired again?

The gpiolib take care per the error handling:

         status = of_gpiochip_add(chip);
         if (status)
                 goto err_remove_chip;

:::
err_remove_chip:
         acpi_gpiochip_remove(chip);
         gpiochip_free_hogs(chip);
         of_gpiochip_remove(chip);