Re: [PATCH v2] Staging: iio: ade7758: expand buf_lock to cover both buffer and state protection

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 25 Jan 2018 22:10:08 +0530
Shreeya Patel <shreeya.patel23498@gmail.com> wrote:

> iio_dev->mlock is to be used only by the IIO core for protecting
> device mode changes between INDIO_DIRECT and INDIO_BUFFER.
> 
> This patch replaces the use of mlock with the already established
> buf_lock mutex.
> 
> Introducing 'unlocked' __ade7758_spi_write_reg_8 and
> __ade7758_spi_read_reg_8 functions to be used by ade7758_write_samp_freq
> and ade7758_read_samp_freq which avoids nested locks and maintains
> atomicity between bus and device frequency changes.
> 
> Signed-off-by: Shreeya Patel <shreeya.patel23498@gmail.com>
Hi Shreeya,

This is now technically correct which is great.
I would make one minor change to make it slightly easier to read.

The read / write frequency functions now require the buf_lock to
be held.  That's not obvious so I would avoid this but moving
the locking inside the functions where it is then clear that
they are taking the unlocked forms of the register read/ write.

This would also then make it clear why the normal locked form
of _read_reg_8 is fine in the read_freq case but not the
write_freq case.  (Hence just use the normal locked form
for the read and don't explicitly take the locks when
reading the frequency - leave it to the register read function)

Thanks,

Jonathan
> ---
> 
> Changes in v2
>   -Add static keyword to newly introduced functions and remove some
> added comments which are not required.
> 
> 
>  drivers/staging/iio/meter/ade7758.h      |  2 +-
>  drivers/staging/iio/meter/ade7758_core.c | 47 +++++++++++++++++++++++---------
>  2 files changed, 35 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7758.h b/drivers/staging/iio/meter/ade7758.h
> index 6ae78d8..2de81b5 100644
> --- a/drivers/staging/iio/meter/ade7758.h
> +++ b/drivers/staging/iio/meter/ade7758.h
> @@ -111,7 +111,7 @@
>   * @trig:		data ready trigger registered with iio
>   * @tx:			transmit buffer
>   * @rx:			receive buffer
> - * @buf_lock:		mutex to protect tx and rx
> + * @buf_lock:		mutex to protect tx, rx, read and write frequency
>   **/
>  struct ade7758_state {
>  	struct spi_device	*us;
> diff --git a/drivers/staging/iio/meter/ade7758_core.c b/drivers/staging/iio/meter/ade7758_core.c
> index 7b7ffe5..fed4684 100644
> --- a/drivers/staging/iio/meter/ade7758_core.c
> +++ b/drivers/staging/iio/meter/ade7758_core.c
> @@ -24,17 +24,25 @@
>  #include "meter.h"
>  #include "ade7758.h"
>  
> -int ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> +static int __ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
>  {
> -	int ret;
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ade7758_state *st = iio_priv(indio_dev);
>  
> -	mutex_lock(&st->buf_lock);
>  	st->tx[0] = ADE7758_WRITE_REG(reg_address);
>  	st->tx[1] = val;
>  
> -	ret = spi_write(st->us, st->tx, 2);
> +	return spi_write(st->us, st->tx, 2);
> +}
> +
> +int ade7758_spi_write_reg_8(struct device *dev, u8 reg_address, u8 val)
> +{
> +	int ret;
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ade7758_state *st = iio_priv(indio_dev);
> +
> +	mutex_lock(&st->buf_lock);
> +	ret = __ade7758_spi_write_reg_8(dev, reg_address, val);
>  	mutex_unlock(&st->buf_lock);
>  
>  	return ret;
> @@ -91,7 +99,7 @@ static int ade7758_spi_write_reg_24(struct device *dev, u8 reg_address,
>  	return ret;
>  }
>  
> -int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> +static int __ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
>  {
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ade7758_state *st = iio_priv(indio_dev);
> @@ -111,7 +119,6 @@ int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
>  		},
>  	};
>  
> -	mutex_lock(&st->buf_lock);
>  	st->tx[0] = ADE7758_READ_REG(reg_address);
>  	st->tx[1] = 0;
>  
> @@ -124,7 +131,19 @@ int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
>  	*val = st->rx[0];
>  
>  error_ret:
> +	return ret;
> +}
> +
> +int ade7758_spi_read_reg_8(struct device *dev, u8 reg_address, u8 *val)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ade7758_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	mutex_lock(&st->buf_lock);
> +	ret = __ade7758_spi_read_reg_8(dev, reg_address, val);
>  	mutex_unlock(&st->buf_lock);
> +
>  	return ret;
>  }
>  
> @@ -470,7 +489,7 @@ static int ade7758_read_samp_freq(struct device *dev, int *val)
>  	int ret;
>  	u8 t;
>  
> -	ret = ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &t);
> +	ret = __ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &t);
>  	if (ret)
>  		return ret;
>  
> @@ -503,14 +522,14 @@ static int ade7758_write_samp_freq(struct device *dev, int val)
>  		goto out;
>  	}
>  
> -	ret = ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &reg);
> +	ret = __ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &reg);
>  	if (ret)
>  		goto out;
>  
>  	reg &= ~(5 << 3);
>  	reg |= t << 5;
>  
> -	ret = ade7758_spi_write_reg_8(dev, ADE7758_WAVMODE, reg);
> +	ret = __ade7758_spi_write_reg_8(dev, ADE7758_WAVMODE, reg);
>  
>  out:
>  	return ret;
> @@ -523,12 +542,13 @@ static int ade7758_read_raw(struct iio_dev *indio_dev,
>  			    long mask)
>  {
>  	int ret;
> +	struct ade7758_state *st = iio_priv(indio_dev);
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SAMP_FREQ:
> -		mutex_lock(&indio_dev->mlock);
> +		mutex_lock(&st->buf_lock);
>  		ret = ade7758_read_samp_freq(&indio_dev->dev, val);
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&st->buf_lock);
>  		return ret;
>  	default:
>  		return -EINVAL;
> @@ -542,14 +562,15 @@ static int ade7758_write_raw(struct iio_dev *indio_dev,
>  			     int val, int val2, long mask)
>  {
>  	int ret;
> +	struct ade7758_state *st = iio_priv(indio_dev);
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SAMP_FREQ:
>  		if (val2)
>  			return -EINVAL;
> -		mutex_lock(&indio_dev->mlock);
> +		mutex_lock(&st->buf_lock);
>  		ret = ade7758_write_samp_freq(&indio_dev->dev, val);
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&st->buf_lock);
>  		return ret;
>  	default:
>  		return -EINVAL;