Re: [PATCH] Staging: iio: meter: ade7759: update locking method for write frequency

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 18 Sep 2017 15:52:40 -0700
Katie Dunne <kdunne@mail.ccsf.edu> 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 an 'unlocked' spi_write_reg_16 function to be used by
> ade7759_write_frequency avoids nested locks and maintains atomicity
> between bus and device frequency changes.
> 
> Based on the solution found in ade7754 patch here:
> https://marc.info/?l=linux-iio&m=149086659008991&w=2
> 
> Signed-off-by: Katie Dunne <kdunne@mail.ccsf.edu>

Very nice.  This is the alternative I was talking about in my review
of a patch for the similar issue in the ad7753 driver earlier.
(Haminshi cc'd).

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with.

Thanks,

Jonathan

> ---
>  drivers/staging/iio/meter/ade7759.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7759.c b/drivers/staging/iio/meter/ade7759.c
> index 1691760..b52d4d7 100644
> --- a/drivers/staging/iio/meter/ade7759.c
> +++ b/drivers/staging/iio/meter/ade7759.c
> @@ -60,7 +60,7 @@
>  /**
>   * struct ade7759_state - device instance specific data
>   * @us:			actual spi_device
> - * @buf_lock:		mutex to protect tx and rx
> + * @buf_lock:		mutex to protect tx and rx and write frequency
>   * @tx:			transmit buffer
>   * @rx:			receive buffer
>   **/
> @@ -89,19 +89,30 @@ static int ade7759_spi_write_reg_8(struct device *dev,
>  	return ret;
>  }
>  
> -static int ade7759_spi_write_reg_16(struct device *dev,
> +/*Unlocked version of ade7759_spi_write_reg_16 function */
> +static int __ade7759_spi_write_reg_16(struct device *dev,
>  		u8 reg_address,
>  		u16 value)
>  {
> -	int ret;
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ade7759_state *st = iio_priv(indio_dev);
>  
> -	mutex_lock(&st->buf_lock);
>  	st->tx[0] = ADE7759_WRITE_REG(reg_address);
>  	st->tx[1] = (value >> 8) & 0xFF;
>  	st->tx[2] = value & 0xFF;
> -	ret = spi_write(st->us, st->tx, 3);
> +	return spi_write(st->us, st->tx, 3);
> +}
> +
> +static int ade7759_spi_write_reg_16(struct device *dev,
> +		u8 reg_address,
> +		u16 value)
> +{
> +	int ret;
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ade7759_state *st = iio_priv(indio_dev);
> +
> +	mutex_lock(&st->buf_lock);
> +	ret = __ade7759_spi_write_reg_16(dev, reg_address, value);
>  	mutex_unlock(&st->buf_lock);
>  
>  	return ret;
> @@ -429,7 +440,7 @@ static ssize_t ade7759_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->buf_lock);
>  
>  	t = 27900 / val;
>  	if (t > 0)
> @@ -447,10 +458,10 @@ static ssize_t ade7759_write_frequency(struct device *dev,
>  	reg &= ~(3 << 13);
>  	reg |= t << 13;
>  
> -	ret = ade7759_spi_write_reg_16(dev, ADE7759_MODE, reg);
> +	ret = __ade7759_spi_write_reg_16(dev, ADE7759_MODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->buf_lock);
>  
>  	return ret ? ret : len;
>  }