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Subject: Re: [PATCH 2/2] iio: ti_am335x_adc: Add continuous sampling support
From: Jonathan Cameron <jic23@kernel.org>
Date: Wed, 18 Sep 2013 10:39:42 +0100
To: "Zubair Lutfullah :" <zubair.lutfullah@gmail.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>
CC: linux-iio@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
        gregkh@linuxfoundation.org
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"Zubair Lutfullah :" <zubair.lutfullah@gmail.com> wrote:
>On Tue, Sep 17, 2013 at 09:27:27PM -0700, Dmitry Torokhov wrote:
>> Hi Zubair,
>> 
>> On Tue, Sep 17, 2013 at 09:44:07AM +0500, Zubair Lutfullah wrote:
>> > +
>> > +	ret = devm_request_threaded_irq(indio_dev->dev.parent,
>> > +				irq,
>> > +				pollfunc_th, pollfunc_bh,
>> > +				flags, indio_dev->name,
>> > +				indio_dev);
>> > +	if (ret)
>> > +		goto error_kfifo_free;
>> > +
>> > +	indio_dev->setup_ops = setup_ops;
>> > +	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
>> > +
>> > +	ret = iio_buffer_register(indio_dev,
>> > +				  indio_dev->channels,
>> > +				  indio_dev->num_channels);
>> > +	if (ret)
>> > +		goto error_free_irq;
>> > +
>> > +	return 0;
>> > +
>> > +error_free_irq:
>> > +	devm_free_irq(indio_dev->dev.parent, irq, indio_dev);
>> 
>> What is the point of using devm_* here if you are doing explicit
>> management of the resource anyway (you explicitly release it in all
>code
>> paths)?
>> 
>> Thanks.
>> 
>> -- 
>> Dmitry
>
>I admit I am unaware at the moment about how it works.
>
>I use devm and simply ignore the error path?
>
>The devm function header description said something about using
>devm_free when freeing. And this is the way I am used to seeing 
>error handling.

The devm interfaces ensure this is all cleaned when the device is removed thus avoiding the need to free the stuff explicitly.
Device will get freed on deliberate remove and on an error from probe. Hence you can drop all calls to devm free. The devm free functions are only needed if you wish to free in order to reallocate. This might happen if you want to change a buffer size for instance.
>
>Zubair

-- 
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