linux-kernel - Re: [PATCH v4] staging: Use buf_lock instead of mlock and Refactor code

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Date:   Sun, 19 Mar 2017 10:15:56 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     simran singhal <singhalsimran0@...il.com>, lars@...afoo.de
Cc:     Michael.Hennerich@...log.com, Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [PATCH v4] staging: Use buf_lock instead of mlock and Refactor
 code

On 18/03/17 18:44, simran singhal wrote:
> The IIO subsystem is redefining iio_dev->mlock to be used by
> the IIO core only for protecting device operating mode changes.
> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
> 
> In this driver, mlock was being used to protect hardware state
> changes. Replace it with buf_lock in the devices global data.
> 
> As buf_lock protects both the adis16060_spi_write() and
> adis16060_spi_read() functions and both are always called in
> pair. First write, then read. Thus, refactor the code to have
> one single function adis16060_spi_write_than_read() which is
> protected by the existing buf_lock.
> 
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
Hi Simran,

A couple of minor comments and opportunity to further improve
the, now simpler, code flow.

Thanks,

Jonathan
> ---
> 
>  v4:
>    -Refactored code 
>    -change commit subject
>    -change commit message
> 
>  drivers/staging/iio/gyro/adis16060_core.c | 37 ++++++++++++-------------------
>  1 file changed, 14 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/staging/iio/gyro/adis16060_core.c b/drivers/staging/iio/gyro/adis16060_core.c
> index c9d46e7..39ddd55 100644
> --- a/drivers/staging/iio/gyro/adis16060_core.c
> +++ b/drivers/staging/iio/gyro/adis16060_core.c
> @@ -40,7 +40,7 @@ struct adis16060_state {
>  
>  static struct iio_dev *adis16060_iio_dev;
>  
> -static int adis16060_spi_write(struct iio_dev *indio_dev, u8 val)
> +static int adis16060_spi_write_than_read(struct iio_dev *indio_dev, u8 val, u16 *val2)
val and val2 often have specific meanings in IIO.  I'd prefer these to be renamed to
val => conf (as it sets the configuration) and val2 => val.
>  {
>  	int ret;
>  	struct adis16060_state *st = iio_priv(indio_dev);
> @@ -48,17 +48,11 @@ static int adis16060_spi_write(struct iio_dev *indio_dev, u8 val)
>  	mutex_lock(&st->buf_lock);
>  	st->buf[2] = val; /* The last 8 bits clocked in are latched */
>  	ret = spi_write(st->us_w, st->buf, 3);
> -	mutex_unlock(&st->buf_lock);
>  
> -	return ret;
> -}
> -
> -static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val)
> -{
> -	int ret;
> -	struct adis16060_state *st = iio_priv(indio_dev);
> -
> -	mutex_lock(&st->buf_lock);
> +	if (ret < 0) {
> +		mutex_unlock(&st->buf_lock);
> +		return ret;
> +	}
>  
>  	ret = spi_read(st->us_r, st->buf, 3);
>  
> @@ -67,10 +61,10 @@ static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val)
>  	 * starts to place data MSB first on the DOUT line at
>  	 * the 6th falling edge of SCLK
>  	 */
> -	if (!ret)
> -		*val = ((st->buf[0] & 0x3) << 12) |
> -			(st->buf[1] << 4) |
> -			((st->buf[2] >> 4) & 0xF);
> +        if (!ret)
Please run checkpatch.pl over your patches.  Looks like
you ended up with spaces instead of a tab in the line above.
> +		*val2 = ((st->buf[0] & 0x3) << 12) |
> +			 (st->buf[1] << 4) |
> +			 ((st->buf[2] >> 4) & 0xF);
>  	mutex_unlock(&st->buf_lock);
>  
>  	return ret;
> @@ -83,20 +77,17 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
>  {
>  	u16 tval = 0;
>  	int ret;
> +	struct adis16060_state *st = iio_priv(indio_dev);
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_RAW:
>  		/* Take the iio_dev status lock */
> -		mutex_lock(&indio_dev->mlock);
> -		ret = adis16060_spi_write(indio_dev, chan->address);
> +		mutex_lock(&st->buf_lock);
> +		ret = adis16060_spi_write_than_read(indio_dev, chan->address, &tval);
>  		if (ret < 0)
>  			goto out_unlock;
>  
> -		ret = adis16060_spi_read(indio_dev, &tval);
> -		if (ret < 0)
This ugly goto construction arguably made sense when there were two of them.  Now
you have only one just bring the mutex_unlock inline and return directly.
> -			goto out_unlock;
> -
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&st->buf_lock);
>  		*val = tval;
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_OFFSET:
> @@ -112,7 +103,7 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
>  	return -EINVAL;
>  
>  out_unlock:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->buf_lock);
>  	return ret;
>  }
>  
>