linux-kernel - Re: [RFC PATCH 1/2] iio: core: implement iio_{claim|release}_direct

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Date:	Sat, 5 Mar 2016 18:02:36 +0000
From:	Jonathan Cameron <jic23@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Alison Schofield <amsfield22@...il.com>,
	outreachy-kernel@...glegroups.com
Cc:	knaack.h@....de, pmeerw@...erw.net, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, Michael.Hennerich@...log.com,
	gregkh@...uxfoundation.org, devel@...verdev.osuosl.org
Subject: Re: [RFC PATCH 1/2] iio: core: implement
 iio_{claim|release}_direct_mode()

On 02/03/16 13:28, Lars-Peter Clausen wrote:
> On 03/01/2016 08:02 PM, Alison Schofield wrote:
>> It is often the case that the driver wants to be sure a device stays
>> in direct mode while it is executing a task or series of tasks.  To
>> accomplish this today, the driver performs this sequence: 1) take the
>> device state lock, 2)verify it is not in a buffered mode, 3) execute
>> some tasks, and 4) release that lock.
>>
>> This patch introduces a pair of helper functions that simplify these
>> steps and make it more semantically expressive.
>>
>> iio_claim_direct_mode()
>>         If the device is not in any buffered mode it is guaranteed
>>         to stay that way until iio_release_direct_mode() is called.
>>
>> iio_release_direct_mode()
>>         Release the claim. Device is no longer guaranteed to stay
>>         in direct mode.
>>
>> Signed-off-by: Alison Schofield <amsfield22@...il.com>
> 
> Looks basically good.
Agreed - nothing to add from me to what Lars has covered here.
Nice to 'hide' the accesses to mlock as well as will cut out the desire
to 'abuse it'.  Amusingly we only just 'fixed' the docs to to say this
element of iio_dev was usable by drivers.  Once we have these new functions
in use throughout the tree, we will want to flip that back again to internal
only.

Jonathan
> 
>> ---
>>  drivers/iio/industrialio-core.c | 39 +++++++++++++++++++++++++++++++++++++++
>>  include/linux/iio/iio.h         |  2 ++
>>  2 files changed, 41 insertions(+)
>>
>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>> index 70cb7eb..f6f0c89 100644
>> --- a/drivers/iio/industrialio-core.c
>> +++ b/drivers/iio/industrialio-core.c
>> @@ -25,6 +25,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/anon_inodes.h>
>>  #include <linux/debugfs.h>
>> +#include <linux/mutex.h>
>>  #include <linux/iio/iio.h>
>>  #include "iio_core.h"
>>  #include "iio_core_trigger.h"
>> @@ -1375,6 +1376,44 @@ void devm_iio_device_unregister(struct device *dev, struct iio_dev *indio_dev)
>>  }
>>  EXPORT_SYMBOL_GPL(devm_iio_device_unregister);
>>  
>> +/**
>> + * iio_claim_direct_mode - Keep device in direct mode
>> + * @indio_dev:	the iio_dev associated with the device
>> + *
>> + * If the device is in direct mode it is guaranteed to
>> + * stay that way until iio_release_direct_mode() is called.
>> + *
>> + * Use with iio_release_direct_mode()
>> + *
>> + * Returns: 0 on success, -EINVAL on failure
>> + */
>> +int iio_claim_direct_mode(struct iio_dev *indio_dev)
> 
> To be consistent with the reset of the API I'd use the iio_device_... prefix
> here, same for the release function.
> 
>> +{
>> +	mutex_lock(&indio_dev->mlock);
>> +
>> +	if (iio_buffer_enabled(indio_dev)) {
>> +		mutex_unlock(&indio_dev->mlock);
>> +		return -EINVAL;
> 
> -EINVAL doesn't make much sense here, -EBUSY is better.
> 
>> +	}
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(iio_claim_direct_mode);
>>