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

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Date:	Sun, 27 Sep 2015 14:31:28 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Vaishali Thakkar <vthakkar1994@...il.com>,
	Karol Wrona <k.wrona@...sung.com>
Cc:	Jonathan Cameron <jic23@...23.retrosnub.co.uk>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>, linux-iio@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: gyro: ssp_gyro_sensor: Use devm_iio_device_register

On 27/09/15 05:16, Vaishali Thakkar wrote:
> On Mon, Sep 21, 2015 at 4:48 PM, Karol Wrona <k.wrona@...sung.com> wrote:
>> On 09/21/2015 11:53 AM, Jonathan Cameron wrote:
>>>
>>>
>>> On 21 September 2015 09:18:39 BST, Karol Wrona <k.wrona@...sung.com> wrote:
>>>> 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.
>>> Not if you want to remove the userspace interface before doing you new function call.  Doing so gives a nasty race.
>> So better leave it out:
>> iio_device_unregister(indio_dev) will disable the buffers and through
>> ops disables the sensor and than remove iio dev ptr from the internal table.
>>
> 
> Sorry for the late reply. Yes, I guess I missed the point that
> 'ssp_register_consumer' is
> used in probe function. And I believe that devm_iio_register is useful
> only when we
> can convert all other functions to their devm counterparts and remove
> function will go
> away.
Yes. Exactly.
> 
> But then why don't we need ssp_deregister_consumer here in the remove function?
> Is it automatically handled by  iio_device_unregister? I guess Karol
> tried to explain
> the same thing but I am still confused. Same case applies for
> ssp_sensors/ssp_dev.c.
We do indeed need an ssp_deregister_consumer function to be called in the remove.
I don't think one currently exists, so that needs fixing.
> 
>>>>
>>>> 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);
>>>>>>
>>>>>
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-iio"
>>>> in
>>>>> the body of a message to majordomo@...r.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>
>>>
>>
> 
> 
> 

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