Re: [PATCH v3] iio: adc: mcp3422: fix locking scope

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 31 Aug 2020 14:59:47 +0200
Angelo Compagnucci <angelo.compagnucci@gmail.com> wrote:

> From: Angelo Compagnucci <angelo.compagnucci@gmail.com>
> 
> Locking should be held for the entire reading sequence involving setting
> the channel, waiting for the channel switch and reading from the
> channel.
> If not, reading from a channel can result mixing with the reading from
> another channel.
> 
> Fixes: 07914c84ba30 ("iio: adc: Add driver for Microchip MCP3422/3/4 high resolution ADC")
> Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
> Signed-off-by: Angelo Compagnucci <angelo@amarulasolutions.com>
> ---
Hi Angelo

Change log?

Given I've just sent a pull request including v2, we are probably now in a mess
if we actually need to use v3.

Jonathan

>  drivers/iio/adc/mcp3422.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/adc/mcp3422.c b/drivers/iio/adc/mcp3422.c
> index d86c0b5d80a3..f96f0cecbcde 100644
> --- a/drivers/iio/adc/mcp3422.c
> +++ b/drivers/iio/adc/mcp3422.c
> @@ -96,16 +96,12 @@ static int mcp3422_update_config(struct mcp3422 *adc, u8 newconfig)
>  {
>  	int ret;
>  
> -	mutex_lock(&adc->lock);
> -
>  	ret = i2c_master_send(adc->i2c, &newconfig, 1);
>  	if (ret > 0) {
>  		adc->config = newconfig;
>  		ret = 0;
>  	}
>  
> -	mutex_unlock(&adc->lock);
> -
>  	return ret;
>  }
>  
> @@ -138,6 +134,8 @@ static int mcp3422_read_channel(struct mcp3422 *adc,
>  	u8 config;
>  	u8 req_channel = channel->channel;
>  
> +	mutex_lock(&adc->lock);
> +
>  	if (req_channel != MCP3422_CHANNEL(adc->config)) {
>  		config = adc->config;
>  		config &= ~MCP3422_CHANNEL_MASK;
> @@ -145,12 +143,18 @@ static int mcp3422_read_channel(struct mcp3422 *adc,
>  		config &= ~MCP3422_PGA_MASK;
>  		config |= MCP3422_PGA_VALUE(adc->pga[req_channel]);
>  		ret = mcp3422_update_config(adc, config);
> -		if (ret < 0)
> +		if (ret < 0) {
> +			mutex_unlock(&adc->lock);
>  			return ret;
> +		}
>  		msleep(mcp3422_read_times[MCP3422_SAMPLE_RATE(adc->config)]);
>  	}
>  
> -	return mcp3422_read(adc, value, &config);
> +	ret = mcp3422_read(adc, value, &config);
> +
> +	mutex_unlock(&adc->lock);
> +
> +	return ret;
>  }
>  
>  static int mcp3422_read_raw(struct iio_dev *iio,