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

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Mon, 31 Aug 2020 15:10:11 +0100
Jonathan Cameron <jic23@kernel.org> wrote:

> 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.

Hi Angelo,

Just found the discussion with Julia.

Unfortunately that went to my work account and yesterday was a holiday in the UK
so I missed it.

Could you spin a patch with the difference between v2 and v3 asap and add
gregkh@linuxfoundation.org to the cc list.  If he prefers it that way I'll ack
and Greg can pick it up directly.

Jonathan

> 
> 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,  
>