Date:	Mon, 28 Sep 2015 15:38:10 +0530
From:	Vaishali Thakkar <vthakkar1994@...il.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	Karol Wrona <k.wrona@...sung.com>,
	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 Mon, Sep 28, 2015 at 6:42 AM, Vaishali Thakkar
<vthakkar1994@...il.com> wrote:
> On Sun, Sep 27, 2015 at 7:01 PM, Jonathan Cameron <jic23@...nel.org> wrote:
>> 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.
>
> Ok. Then I'll send patches for both of these files.

Sorry, probably I was not clear enough in my last mail. I mean I'll
send patches patches
once we will have something like 'ssp_deregister_consumer'. But is
there anyone who
is working on this? Is it possible to introduce devm counterpart of the same?
How much will it be useful [taking note that there are only 3-4 files
which are using it]?

>>>>>>
>>>>>> 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
>>>>>>>
>>>>>
>>>>
>>>
>>>
>>>
>>
>
>
>
> --
> Vaishali



-- 
Vaishali
--
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