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

SIMRAN SINGHAL
2017-03-28T17:25:22Z

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.

> 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.

> 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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