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

SIMRAN SINGHAL
2017-03-30T20:13:20Z

On Fri, Mar 31, 2017 at 1:18 AM, Jonathan Cameron
<jic23@jic23.retrosnub.co.uk> wrote:
>
>
> On 30 March 2017 19:44:26 BST, SIMRAN SINGHAL <singhalsimran0@gmail.com> wrote:
>>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.
>
> 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@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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