On Sun, Sep 24, 2017 at 7:47 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
> On Mon, 18 Sep 2017 12:29:52 +0530
> Himanshi Jain <himshijain.hj@xxxxxxxxx> wrote:
>
>> Replace driver usage of mlock with driver private lock to meet the new
>> model where usage of iio_dev->mlock is being redefined as protecting
>> operating mode changes(changes between BUFFER* and DIRECT modes).
>>
>> Signed-off-by: Himanshi Jain <himshijain.hj@xxxxxxxxx>
>
> A well presented patch making a sensible change. My only thought here
> is that ultimately we could cover bother the buffer protection and
> the state protection with a single lock.
>
> Hmm. The new lock (as was the old mlock code) is providing protection
> to ensure we end up with consistent state when changing the
> sampling frequency between the sampling frequency and the
> bus clock speed (which has different maximum values depending
> on the current sampling frequency). In similar cases we have
> expanded the meaning on the buffer lock to fulfil both roles
> - that could be done here as well, although you have to be careful
> about deadlocks.
>
I have understood how to use a single lock for both the purposes as you have
quoted in Katie's patch too i.e. by making an unlocked version of the function
ade7753_spi_write_reg_16(). And since the function is not publicly available
to be used, an unlocked version will not create any issue(which is why I am
assuming, we are not using nested locks - Please correct me if I am wrong.)
I will submit a new patch with a single lock.
> On reflection I think this patch is worthwhile applying even
> if this new lock gets dropped again in some later rework of this
> driver.
>
> Applied to the togreg branch of iio.git and pushed out as testing for
> the autobuilders to play with it.
>
Thank you for reviewing and applying the patch and guiding for a better logical
solution.
> Thanks,
>
> Jonathan
>> ---
>> 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 ce26abdea..745c5a6 100644
>> --- a/drivers/staging/iio/meter/ade7753.c
>> +++ b/drivers/staging/iio/meter/ade7753.c
>> @@ -81,10 +81,12 @@
>> * @tx: transmit buffer
>> * @rx: receive buffer
>> * @buf_lock: mutex to protect tx and rx
>> + * @lock: protect sensor data
>> **/
>> struct ade7753_state {
>> struct spi_device *us;
>> struct mutex buf_lock;
>> + struct mutex lock; /* protect sensor data */
>> u8 tx[ADE7753_MAX_TX] ____cacheline_aligned;
>> u8 rx[ADE7753_MAX_RX];
>> };
>> @@ -483,7 +485,7 @@ 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)
>> @@ -504,7 +506,7 @@ 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;
>> }
>> @@ -580,6 +582,7 @@ 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;
>
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