linux-kernel - Re: [PATCH 2/2] iio: ti_am335x_adc: Add continuous sampling support

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Message-ID: <b37c9a0e-36ed-49bf-bb68-453c7b07b437@email.android.com>
Date:	Wed, 18 Sep 2013 17:12:02 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	"Zubair Lutfullah :" <zubair.lutfullah@...il.com>,
	linux-iio@...r.kernel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 2/2] iio: ti_am335x_adc: Add continuous sampling support



Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
>On Wed, Sep 18, 2013 at 10:39:42AM +0100, Jonathan Cameron wrote:
>> 
>> 
>> "Zubair Lutfullah :" <zubair.lutfullah@...il.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.
>
>However in this case such conversion us dangerous. With all but IRQ
>resource managed by the traditional methods they will be released first
>with IRQ handler deregistered very last. Therefore if device is not
>properly quiesced IRQ raised during driver unbinding is likely to
>result
>in kernel oops.
>
>IOW devm_request_irq() is very often evil (it is still useful if _all_
>your resources are managed by devm_*).
>
>In case of your driver I'd recommend switching to
>request_irq()/free_irq() instead.
>
>Thanks.

Pretty much all resources are devm managed in here

https://git.kernel.org/cgit/linux/kernel/git/jic23/iio.git/tree/drivers/iio/adc/ti_am335x_adc.c?h=togreg&id=7a1aeba7ed0d5a1e83fd5a8ee2a2869430d40347

There is a left over calloc which could be converted but that's it.
-- 
Sent from my Android phone with K-9 Mail. Please excuse my brevity.
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