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

[SIMRAN SINGHAL <singhalsimran0@gmail.com>]

On Fri, Mar 31, 2017 at 12:02 AM, Jonathan Cameron <jic23@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@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.

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