Re: [PATCH v4] iio: adc: mcp3911: simplify code with guard macro

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 06 Dec 2023 19:39:04 +0100
Marcus Folkesson <marcus.folkesson@gmail.com> wrote:

> Use the guard(mutex) macro for handle mutex lock/unlocks.
> 
> Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Various changes inline - most are focused around simplifying the
path for any given flow through the code.

Rather than going for a v5 - I've applied this with the following diff on top
diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
index dfcb6cb7570f..7a32e7a1be9d 100644
--- a/drivers/iio/adc/mcp3911.c
+++ b/drivers/iio/adc/mcp3911.c
@@ -317,7 +317,7 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
                            int *val2, long mask)
 {
        struct mcp3911 *adc = iio_priv(indio_dev);
-       int ret = -EINVAL;
+       int ret;
 
        guard(mutex)(&adc->lock);
        switch (mask) {
@@ -331,17 +331,23 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_OFFSET:
                ret = adc->chip->get_offset(adc, channel->channel, val);
-               return (ret) ? ret : IIO_VAL_INT;
+               if (ret)
+                       return ret;
+
+               return IIO_VAL_INT;
        case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
                ret = adc->chip->get_osr(adc, val);
-               return (ret) ? ret : IIO_VAL_INT;
+               if (ret)
+                       return ret;
+
+               return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                *val = mcp3911_scale_table[ilog2(adc->gain[channel->channel])][0];
                *val2 = mcp3911_scale_table[ilog2(adc->gain[channel->channel])][1];
                return IIO_VAL_INT_PLUS_NANO;
+       default:
+               return -EINVAL;
        }
-
-       return ret;
 }
 
 static int mcp3911_write_raw(struct iio_dev *indio_dev,
@@ -361,7 +367,7 @@ static int mcp3911_write_raw(struct iio_dev *indio_dev,
                                return adc->chip->set_scale(adc, channel->channel, i);
                        }
                }
-               break;
+               return -EINVAL;
        case IIO_CHAN_INFO_OFFSET:
                if (val2 != 0)
                        return -EINVAL;
@@ -373,9 +379,10 @@ static int mcp3911_write_raw(struct iio_dev *indio_dev,
                                return adc->chip->set_osr(adc, i);
                        }
                }
-               break;
+               return -EINVAL;
+       default:
+               return -EINVAL;
        }
-       return -EINVAL;
 }

hope that's ok with you!

Jonathan
> ---
> Changes in v4:
> - Remove unreachable breaks
> - Link to v3: https://lore.kernel.org/r/20231205-mcp3911-guard-v3-1-df83e956d1e9@gmail.com
> 
> Changes in v3:
> - Return early in good paths as well
> - Rebase against master
> - Link to v2: https://lore.kernel.org/r/20231127-mcp3911-guard-v2-1-9462630dca1e@gmail.com
> 
> Changes in v2:
> - Return directly instead of goto label
> - Link to v1: https://lore.kernel.org/r/20231125-mcp3911-guard-v1-1-2748d16a3f3f@gmail.com
> ---
>  drivers/iio/adc/mcp3911.c | 55 +++++++++++++----------------------------------
>  1 file changed, 15 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
> index d864558bc087..dfcb6cb7570f 100644
> --- a/drivers/iio/adc/mcp3911.c
> +++ b/drivers/iio/adc/mcp3911.c
> @@ -7,6 +7,7 @@
>   */
>  #include <linux/bitfield.h>
>  #include <linux/bits.h>
> +#include <linux/cleanup.h>
>  #include <linux/clk.h>
>  #include <linux/delay.h>
>  #include <linux/err.h>
> @@ -318,44 +319,28 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
>  	struct mcp3911 *adc = iio_priv(indio_dev);
>  	int ret = -EINVAL;
>  
> -	mutex_lock(&adc->lock);
> +	guard(mutex)(&adc->lock);
>  	switch (mask) {
>  	case IIO_CHAN_INFO_RAW:
>  		ret = mcp3911_read(adc,
>  				   MCP3911_CHANNEL(channel->channel), val, 3);
>  		if (ret)
> -			goto out;
> +			return ret;
>  
>  		*val = sign_extend32(*val, 23);
> -
> -		ret = IIO_VAL_INT;
> -		break;
> -
> +		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_OFFSET:
> -
>  		ret = adc->chip->get_offset(adc, channel->channel, val);
> -		if (ret)
> -			goto out;
> -
> -		ret = IIO_VAL_INT;
> -		break;
> +		return (ret) ? ret : IIO_VAL_INT;

Don't do this. The ternary just makes it harder to read.

		if (ret)
			return ret;

		return IIO_VAL_INT;

+ the brackets around (ret) are unnecessary.

>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>  		ret = adc->chip->get_osr(adc, val);
> -		if (ret)
> -			goto out;
> -
> -		ret = IIO_VAL_INT;
> -		break;
> -
> +		return (ret) ? ret : IIO_VAL_INT;

here as well

>  	case IIO_CHAN_INFO_SCALE:
>  		*val = mcp3911_scale_table[ilog2(adc->gain[channel->channel])][0];
>  		*val2 = mcp3911_scale_table[ilog2(adc->gain[channel->channel])][1];
> -		ret = IIO_VAL_INT_PLUS_NANO;
> -		break;
> +		return IIO_VAL_INT_PLUS_NANO;
>  	}
>  
> -out:
> -	mutex_unlock(&adc->lock);
>  	return ret;

This ret is only reachable if we don't hit any of the switch entries so
better to add add a default and return -EINVAL to make that apparent and
let the compiler detect if we are missing a return earlier.

>  }
>  
> @@ -364,9 +349,8 @@ static int mcp3911_write_raw(struct iio_dev *indio_dev,
>  			     int val2, long mask)
>  {
>  	struct mcp3911 *adc = iio_priv(indio_dev);
> -	int ret = -EINVAL;
>  
> -	mutex_lock(&adc->lock);
> +	guard(mutex)(&adc->lock);
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SCALE:
>  		for (int i = 0; i < MCP3911_NUM_SCALES; i++) {
> @@ -374,32 +358,24 @@ static int mcp3911_write_raw(struct iio_dev *indio_dev,
>  			    val2 == mcp3911_scale_table[i][1]) {
>  
>  				adc->gain[channel->channel] = BIT(i);
> -				ret = adc->chip->set_scale(adc, channel->channel, i);
> +				return adc->chip->set_scale(adc, channel->channel, i);
>  			}
>  		}
>  		break;
>  	case IIO_CHAN_INFO_OFFSET:
> -		if (val2 != 0) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -
> -		ret = adc->chip->set_offset(adc, channel->channel, val);
> -		break;
> +		if (val2 != 0)
> +			return -EINVAL;
>  
> +		return adc->chip->set_offset(adc, channel->channel, val);
>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>  		for (int i = 0; i < ARRAY_SIZE(mcp3911_osr_table); i++) {
>  			if (val == mcp3911_osr_table[i]) {
> -				ret = adc->chip->set_osr(adc, i);
> -				break;
> +				return adc->chip->set_osr(adc, i);
>  			}
>  		}
>  		break;

return -INVAL; here and similar above to simplify the flow.

>  	}
> -
> -out:
> -	mutex_unlock(&adc->lock);
> -	return ret;
> +	return -EINVAL;

Move this to a default.

>  }
>  
>  static int mcp3911_calc_scale_table(struct mcp3911 *adc)
> @@ -532,7 +508,7 @@ static irqreturn_t mcp3911_trigger_handler(int irq, void *p)
>  	int i = 0;
>  	int ret;
>  
> -	mutex_lock(&adc->lock);
> +	guard(mutex)(&adc->lock);
>  	adc->tx_buf = MCP3911_REG_READ(MCP3911_CHANNEL(0), adc->dev_addr);
>  	ret = spi_sync_transfer(adc->spi, xfer, ARRAY_SIZE(xfer));
>  	if (ret < 0) {
> @@ -549,7 +525,6 @@ static irqreturn_t mcp3911_trigger_handler(int irq, void *p)
>  	iio_push_to_buffers_with_timestamp(indio_dev, &adc->scan,
>  					   iio_get_time_ns(indio_dev));
>  out:
> -	mutex_unlock(&adc->lock);
>  	iio_trigger_notify_done(indio_dev->trig);
>  
>  	return IRQ_HANDLED;
> 
> ---
> base-commit: 33cc938e65a98f1d29d0a18403dbbee050dcad9a
> change-id: 20231125-mcp3911-guard-866591e2c947
> 
> Best regards,