On 17/03/17 09:32, Gargi Sharma wrote:
> On Mon, Mar 13, 2017 at 5:30 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
>>
>> On 03/12/2017 02:32 PM, 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.
>>>
>>> Fix some coding style issues related to white space also.
>>>
>>> Signed-off-by: simran singhal <singhalsimran0@xxxxxxxxx>
>>> ---
>>> drivers/staging/iio/meter/ade7753.c | 14 ++++++++------
>>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>> index dfd8b71..ca99d82 100644
>>> --- a/drivers/staging/iio/meter/ade7753.c
>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>> @@ -81,12 +81,14 @@
>>> * @tx: transmit buffer
>>> * @rx: receive buffer
>>> * @buf_lock: mutex to protect tx and rx
>>> + * @lock: protect sensor state
>>
>> It might make sense to reuse the existing lock which currently protects the
>> read/write functions. You can do this by introducing a variant of
>> ade7753_spi_{read,write}_reg_16() that does not take a lock and use these to
>> implement the read-modify-write cycle in a protected section.
>
> There are other read/write functions for example,
> ade7753_spi_{read/write}_reg_8 that use the mutex as well. Should a
> variant of these functions be introduced as well? Also, how does one
> go about implementing RMW inside a protected section.
Hmm. Simran has also been progressing with patches for this.
You raise a good question. There are other read/modify/write sequences in
the driver. They don't have the same issue with potentially deadlocking
against the buf lock as they are all using the spi subsystems provisions
for small write/read cycles where buffer protection is handled internally.
So let us address the cases in turn:
static int ade7753_reset(struct device *dev)
{
u16 val;
int ret;
ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
if (ret)
return ret;
val |= BIT(6); /* Software Chip Reset */
return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
}
This is only called in the device initialization. At that point
we should be fine in assuming no parallel calls. Crucial point
is it is before the call to iio_device_register which exposes
the userspace interfaces.
static int ade7753_set_irq(struct device *dev, bool enable)
{
int ret;
u8 irqen;
ret = ade7753_spi_read_reg_8(dev, ADE7753_IRQEN, &irqen);
if (ret)
goto error_ret;
if (enable)
irqen |= BIT(3); /* Enables an interrupt when a data is
* present in the waveform register
*/
else
irqen &= ~BIT(3);
ret = ade7753_spi_write_reg_8(dev, ADE7753_IRQEN, irqen);
error_ret:
return ret;
}
This one is actually safe because it is the only function that
modifies that particular register.
/* Power down the device */
static int ade7753_stop_device(struct device *dev)
{
u16 val;
int ret;
ret = ade7753_spi_read_reg_16(dev, ADE7753_MODE, &val);
if (ret)
return ret;
val |= BIT(4); /* AD converters can be turned off */
return ade7753_spi_write_reg_16(dev, ADE7753_MODE, val);
}
Only called in remove (after userspace interfaces have been
removed by the iio_device_unregister call so also should not
be running concurrently with much else.
So I think all the other cases are safe. Perhaps it would have
been better to have had a lock around them, purely to make
the code more resilient against future changes though.
Probably a job to do as part of a larger scale pile of work
on that driver rather than as a one off patch.
Jonathan
>
>
>>
>> Looking through the driver there seem to be other places as well that do
>> read-modify-write that should be protected by a lock, but currently are not.
>> This might be a good task.
>
> Am I right in understanding that we want to introduce mutex lock for
> writes in other drivers as well?
>
> Thanks,
> Gargi
>>
>>> **/
>>> struct ade7753_state {
>>> - struct spi_device *us;
>>> - struct mutex buf_lock;
>>> - u8 tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>> - u8 rx[ADE7753_MAX_RX];
>>> + 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];
>>> };
>>>
>>> static int ade7753_spi_write_reg_8(struct device *dev,
>>> @@ -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;
>>> }
>>>
>>
>> --
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