linux-kernel - Re: [PATCH] iio: gyro: ssp_gyro_sensor: Use devm_iio_device

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Date:	Mon, 21 Sep 2015 10:18:39 +0200
From:	Karol Wrona <k.wrona@...sung.com>
To:	Jonathan Cameron <jic23@...nel.org>,
	Vaishali Thakkar <vthakkar1994@...il.com>
Cc:	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: gyro: ssp_gyro_sensor: Use devm_iio_device_register

On 09/20/2015 09:18 PM, Jonathan Cameron wrote:
> On 14/09/15 17:08, Vaishali Thakkar wrote:
>> Use resourced managed function devm_iio_device_register to
>> make error path simpler. To be compatible with the change,
>> the remove function is removed as it is now redundant.
>>
>> Signed-off-by: Vaishali Thakkar <vthakkar1994@...il.com>
> This patch is reasonable, but makes me wonder if there is an issue
> in the remove path for this driver.  It relies on the ssp_sensors common
> module.  That in ssp_spi.c uses the fact ssp_register_consumer
> has saved the struct iio_dev into a local array in the core driver.
> I think this means that a remove of this function will leave a possible
> null pointer de reference.
You are right. In this case we need something like
ssp_deregister_consumer(...) in ssp_dev.c. So I think that "remove func"
should stay. Of course we can switch to devm iio register.

Also the same can (rather should) be done for accelerometer sensor
(ssp_accel_sensor.c).

Vaishali, if you want please feel free and send patch.

> 
> Now I suspect that case doesn't actually occur because the relevant
> device elements are disabled whenever this module is removed.  Having
> said that we might expect an ssp_unregister_consumer function that
> sets the relevant pointer back to null on removal so as to avoid
> any possible race conditions around driver removal / reprobing.
> A spot of defensive programming rather than necessarily a bug to be
> fixed!
> 
> One little process thing. This driver was written by Karol so patches
> should probably always cc Karol as well as the more general
> maintainer / reviewers for IIO.  Added cc.
> 
> Jonathan
>> ---
>>  drivers/iio/gyro/ssp_gyro_sensor.c | 12 +-----------
>>  1 file changed, 1 insertion(+), 11 deletions(-)
>>
>> diff --git a/drivers/iio/gyro/ssp_gyro_sensor.c b/drivers/iio/gyro/ssp_gyro_sensor.c
>> index 0a8afdd..ac88de7 100644
>> --- a/drivers/iio/gyro/ssp_gyro_sensor.c
>> +++ b/drivers/iio/gyro/ssp_gyro_sensor.c
>> @@ -134,7 +134,7 @@ static int ssp_gyro_probe(struct platform_device *pdev)
>>  
>>  	platform_set_drvdata(pdev, indio_dev);
>>  
>> -	ret = iio_device_register(indio_dev);
>> +	ret = devm_iio_device_register(&pdev->dev, indio_dev);
>>  	if (ret < 0)
>>  		return ret;
>>  
>> @@ -144,21 +144,11 @@ static int ssp_gyro_probe(struct platform_device *pdev)
>>  	return 0;
>>  }
>>  
>> -static int ssp_gyro_remove(struct platform_device *pdev)
>> -{
>> -	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>> -
>> -	iio_device_unregister(indio_dev);
>> -
>> -	return 0;
>> -}
>> -
>>  static struct platform_driver ssp_gyro_driver = {
>>  	.driver = {
>>  		.name = SSP_GYROSCOPE_NAME,
>>  	},
>>  	.probe = ssp_gyro_probe,
>> -	.remove = ssp_gyro_remove,
>>  };
>>  
>>  module_platform_driver(ssp_gyro_driver);
>>
> 
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