linux-kernel - Re: [Outreachy kernel] [PATCH v4] staging: iio: ade7753: Replace mlock with driver private lock

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Message-ID: <20170323192116.GA6614@d830.WORKGROUP>
Date:   Thu, 23 Mar 2017 12:21:17 -0700
From:   Alison Schofield <amsfield22@...il.com>
To:     simran singhal <singhalsimran0@...il.com>
Cc:     lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
        knaack.h@....de, pmeerw@...erw.net, gregkh@...uxfoundation.org,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [Outreachy kernel] [PATCH v4] staging: iio: ade7753: Replace
 mlock with driver private lock

On Fri, Mar 24, 2017 at 12:05:20AM +0530, 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 a lock in the devices global data.

Hi Simran,

Please post all revision histories below the --- not just the most
recent.

Does this lock enforce the needed "atomicity" in the write_frequency
function? I read Jonathans comment on a previous revision about
"ensuring the spi bus frequency and sampling frequency of the device
are changed in an atomic fashion"

Is it possible for another spi bus transaction (read or write) to
occur between the read and write in write_frequency?  

alisons
> 
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
> ---
> 
>  v4:
>    -Add mutex_init
> 
>  drivers/staging/iio/meter/ade7753.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
> index b71fbd3..30aebaf 100644
> --- a/drivers/staging/iio/meter/ade7753.c
> +++ b/drivers/staging/iio/meter/ade7753.c
> @@ -80,11 +80,13 @@
>   * @us:         actual spi_device
>   * @tx:         transmit buffer
>   * @rx:         receive buffer
> + * @lock:       protect sensor state
>   * @buf_lock:       mutex to protect tx and rx
>   **/
>  struct ade7753_state {
>  	struct spi_device   *us;
>  	struct mutex        buf_lock;
> +	struct mutex	    lock;  /* protect sensor state */
>  	u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>  	u8          rx[ADE7753_MAX_RX];
>  };
> @@ -484,7 +486,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	if (!val)
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->lock);
>  
>  	t = 27900 / val;
>  	if (t > 0)
> @@ -505,7 +507,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>  	ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>  
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->lock);
>  
>  	return ret ? ret : len;
>  }
> @@ -581,6 +583,7 @@ static int ade7753_probe(struct spi_device *spi)
>  	st = iio_priv(indio_dev);
>  	st->us = spi;
>  	mutex_init(&st->buf_lock);
> +	mutex_init(&st->lock);
>  
>  	indio_dev->name = spi->dev.driver->name;
>  	indio_dev->dev.parent = &spi->dev;
> -- 
> 2.7.4
> 
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