Re: [PATCH v6] Staging: iio: ade7758: Expand buf_lock to cover both buffer and state protection

[Jonathan Cameron <jic23@kernel.org>]

On Tue,  6 Feb 2018 22:31:57 +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' forms of read and write registers. The
> read/write frequency functions now require buf_lock to be held.
> That's not obvious so 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.
> 
> It isn't readily apparent that write frequency function requires
> the locks to be taken, so move it inside the function to where it
> is required to protect.
> 
> Also, the read raw does not require iio_dev->mlock for
> reads. It can run concurrently as resource protection is handled
> by buf_lock in read register.
> 
> Signed-off-by: Shreeya Patel <shreeya.patel23498@gmail.com>
Applied to the togreg branch of iio.git.
Pushed out as testing for the autobuilders at 0day.org an
others to check we didn't get anything wrong.

I'll push out as a non rebasing tree next weekend as I'm offline
most of this week so won't be able to do it before then.

Jonathan

> ---
> 
> Changes in v2
>   -Add static keyword to newly introduced functions and remove some
> added comments which are not required.
> 
> Changes in v3
>   -Remove some useless mlocks and send it as another patch.
> Also make the necessary change in the current patch associated with 
> the new patch with commit id 88eba33. Make commit message more 
> appropriate.
> 
> Changes in v4
>   -Write frequency function do not require lock so move it inside
> the function to where it is required to protect.
> 
> Changes in v5
>   -Remove goto statement and make the code to return -EINVAL there
> itself.
> 
> Changes in v6
>   -Merge patch with commit id 88eba33 with this patch. Also make
> the changed function definition same as before.
>  
>  drivers/staging/iio/meter/ade7758.h      |  2 +-
>  drivers/staging/iio/meter/ade7758_core.c | 52 +++++++++++++++++++++++---------
>  2 files changed, 39 insertions(+), 15 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..4e0dbf5 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;
>  }
>  
> @@ -484,6 +503,8 @@ static int ade7758_write_samp_freq(struct device *dev, int val)
>  {
>  	int ret;
>  	u8 reg, t;
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ade7758_state *st = iio_priv(indio_dev);
>  
>  	switch (val) {
>  	case 26040:
> @@ -499,20 +520,23 @@ static int ade7758_write_samp_freq(struct device *dev, int val)
>  		t = 3;
>  		break;
>  	default:
> -		ret = -EINVAL;
> -		goto out;
> +		return -EINVAL;
>  	}
>  
> -	ret = ade7758_spi_read_reg_8(dev, ADE7758_WAVMODE, &reg);
> +	mutex_lock(&st->buf_lock);
> +
> +	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:
> +	mutex_unlock(&st->buf_lock);
> +
>  	return ret;
>  }
>  
> @@ -526,9 +550,9 @@ static int ade7758_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SAMP_FREQ:
> -		mutex_lock(&indio_dev->mlock);
> +
>  		ret = ade7758_read_samp_freq(&indio_dev->dev, val);
> -		mutex_unlock(&indio_dev->mlock);
> +
>  		return ret;
>  	default:
>  		return -EINVAL;
> @@ -547,9 +571,9 @@ static int ade7758_write_raw(struct iio_dev *indio_dev,
>  	case IIO_CHAN_INFO_SAMP_FREQ:
>  		if (val2)
>  			return -EINVAL;
> -		mutex_lock(&indio_dev->mlock);
> +
>  		ret = ade7758_write_samp_freq(&indio_dev->dev, val);
> -		mutex_unlock(&indio_dev->mlock);
> +
>  		return ret;
>  	default:
>  		return -EINVAL;