[Outreachy kernel] [PATCH v4] staging: iio: ade7753: Replace mlock with driver private lock

[SIMRAN SINGHAL]

On Fri, Mar 31, 2017 at 1:18 AM, Jonathan Cameron
<jic23 at jic23.retrosnub.co.uk> wrote:
>
>
> On 30 March 2017 19:44:26 BST, SIMRAN SINGHAL <singhalsimran0 at gmail.com> wrote:
>>On Fri, Mar 31, 2017 at 12:02 AM, Jonathan Cameron <jic23 at kernel.org>
>>wrote:
>>> On 28/03/17 19:37, Alison Schofield wrote:
>>>> On Tue, Mar 28, 2017 at 10:55:17PM +0530, SIMRAN SINGHAL wrote:
>>>>> On Fri, Mar 24, 2017 at 12:51 AM, Alison Schofield
>><amsfield22 at gmail.com> wrote:
>>>>>> On Fri, Mar 24, 2017 at 12:05:20AM +0530, simran singhal wrote:
>>>>>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>>>>>> the IIO core only for protecting device operating mode changes.
>>>>>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>>>>>
>>>>>>> In this driver, mlock was being used to protect hardware state
>>>>>>> changes.  Replace it with a lock in the devices global data.
>>>>>>
>>>>>> Hi Simran,
>>>>>>
>>>>>> Please post all revision histories below the --- not just the most
>>>>>> recent.
>>>>>>
>>>>> Sorry, will not repeat this.
>>>>>
>>>>>> Does this lock enforce the needed "atomicity" in the
>>write_frequency
>>>>>> function? I read Jonathans comment on a previous revision about
>>>>>> "ensuring the spi bus frequency and sampling frequency of the
>>device
>>>>>> are changed in an atomic fashion"
>>>>>>
>>>>>
>>>>> By introducing another lock I am protecting read_modify_write and
>>>>> in this way also protecting the designated register that we are
>>about
>>>>> to write.
>>>>
>>>> I see it protecting this path from being re-entered.  My uncertainty
>>>> is about other paths to read/write.
>>>>
>>>>>
>>>>>> Is it possible for another spi bus transaction (read or write) to
>>>>>> occur between the read and write in write_frequency?
>>>>>>
>>>>>
>>>>> Gargi has also come up with a solution.
>>>>>
>>https://groups.google.com/forum/#!topic/outreachy-kernel/kzE9CrI5Bd8
>>>>>
>>>>> Should I do like her as her's also seem correct or go ahead with
>>this.
>>>>
>>>> My suggestion would be to wait for feedback on Gargi's patch.
>>>> (See the Outreachy log about creating similar solutions.)
>>>>
>>>> We will not be able to close on this set of patches during the
>>>> Outreachy application window.  You can continue to push for closure
>>>> beyond the March 30th date as your time allows :)
>>>>
>>> It is a close choice between the two approaches. In some ways
>>> yours is easier to follow, but Gargi's is more elegant.
>>>
>>> Lets go with that one for consistency across similar drivers,
>>> but if you had been the original author and done it this way
>>> I certainly wouldn't bother asking you to change it!
>>
>>Yes, jonathan I am the original author.
>
> Sorry, I meant of the driver rather than this improvement.
>
By reading your pervious comment, I got what you mean!!
For consistency, I will do it in the same way Gargi did.

> Jonathan
>>
>>>
>>> So in conclusion both patches are good.
>>>
>>> Jonathan
>>>
>>>> Thanks,
>>>> alisons
>>>>
>>>>>
>>>>>> alisons
>>>>>>>
>>>>>>> Signed-off-by: simran singhal <singhalsimran0 at gmail.com>
>>>>>>> ---
>>>>>>>
>>>>>>>  v4:
>>>>>>>    -Add mutex_init
>>>>>>>
>>>>>>>  drivers/staging/iio/meter/ade7753.c | 7 +++++--
>>>>>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/staging/iio/meter/ade7753.c
>>b/drivers/staging/iio/meter/ade7753.c
>>>>>>> index b71fbd3..30aebaf 100644
>>>>>>> --- a/drivers/staging/iio/meter/ade7753.c
>>>>>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>>>>>> @@ -80,11 +80,13 @@
>>>>>>>   * @us:         actual spi_device
>>>>>>>   * @tx:         transmit buffer
>>>>>>>   * @rx:         receive buffer
>>>>>>> + * @lock:       protect sensor state
>>>>>>>   * @buf_lock:       mutex to protect tx and rx
>>>>>>>   **/
>>>>>>>  struct ade7753_state {
>>>>>>>       struct spi_device   *us;
>>>>>>>       struct mutex        buf_lock;
>>>>>>> +     struct mutex        lock;  /* protect sensor state */
>>>>>>>       u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>>>>>       u8          rx[ADE7753_MAX_RX];
>>>>>>>  };
>>>>>>> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct
>>device *dev,
>>>>>>>       if (!val)
>>>>>>>               return -EINVAL;
>>>>>>>
>>>>>>> -     mutex_lock(&indio_dev->mlock);
>>>>>>> +     mutex_lock(&st->lock);
>>>>>>>
>>>>>>>       t = 27900 / val;
>>>>>>>       if (t > 0)
>>>>>>> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct
>>device *dev,
>>>>>>>       ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>>>>>
>>>>>>>  out:
>>>>>>> -     mutex_unlock(&indio_dev->mlock);
>>>>>>> +     mutex_unlock(&st->lock);
>>>>>>>
>>>>>>>       return ret ? ret : len;
>>>>>>>  }
>>>>>>> @@ -581,6 +583,7 @@ static int ade7753_probe(struct spi_device
>>*spi)
>>>>>>>       st = iio_priv(indio_dev);
>>>>>>>       st->us = spi;
>>>>>>>       mutex_init(&st->buf_lock);
>>>>>>> +     mutex_init(&st->lock);
>>>>>>>
>>>>>>>       indio_dev->name = spi->dev.driver->name;
>>>>>>>       indio_dev->dev.parent = &spi->dev;
>>>>>>> --
>>>>>>> 2.7.4
>>>>>>>
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>>>
>
> --
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