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

[Jonathan Cameron]

On 30 March 2017 19:44:26 BST, SIMRAN SINGHAL <singhalsimran0@xxxxxxxxx> wrote:
>On Fri, Mar 31, 2017 at 12:02 AM, Jonathan Cameron <jic23@xxxxxxxxxx>
>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@xxxxxxxxx> 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.

Jonathan
>
>>
>> So in conclusion both patches are good.
>>
>> Jonathan
>>
>>> Thanks,
>>> alisons
>>>
>>>>
>>>>> alisons
>>>>>>
>>>>>> Signed-off-by: simran singhal <singhalsimran0@xxxxxxxxx>
>>>>>> ---
>>>>>>
>>>>>>  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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