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

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Date:	Sun, 27 Sep 2015 09:46:55 +0530
From:	Vaishali Thakkar <vthakkar1994@...il.com>
To:	Karol Wrona <k.wrona@...sung.com>
Cc:	Jonathan Cameron <jic23@...23.retrosnub.co.uk>,
	Jonathan Cameron <jic23@...nel.org>,
	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 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.

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.

>>>
>>> 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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>>> in
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>>>>
>>
>



-- 
Vaishali
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