linux-kernel - Re: [PATCH v4 07/17] iio: adc: ad7768-1: remove unnecessary locking

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Message-ID: <20250308132420.29d8dc90@jic23-huawei>
Date: Sat, 8 Mar 2025 13:24:20 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Jonathan Santos <Jonathan.Santos@...log.com>
Cc: <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
 <lars@...afoo.de>, <Michael.Hennerich@...log.com>,
 <marcelo.schmitt@...log.com>, <robh@...nel.org>, <krzk+dt@...nel.org>,
 <conor+dt@...nel.org>, <linus.walleij@...aro.org>, <brgl@...ev.pl>,
 <lgirdwood@...il.com>, <broonie@...nel.org>, <dlechner@...libre.com>,
 <marcelo.schmitt1@...il.com>, <jonath4nns@...il.com>
Subject: Re: [PATCH v4 07/17] iio: adc: ad7768-1: remove unnecessary locking

On Thu, 6 Mar 2025 18:01:51 -0300
Jonathan Santos <Jonathan.Santos@...log.com> wrote:

> The current locking is only preventing a triggered buffer Transfer and a
> debugfs register access from happening at the same time. If a register
> access happens during a buffered read, the action is doomed to fail anyway,
> since we need to write a magic value to exit continuous read mode.
> 
> Remove locking from the trigger handler and use
> iio_device_claim_direct_mode() instead in the register access function.
> 
> Reviewed-by: David Lechner <dlechner@...libre.com>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
I don't really want more of the old school direct_mode calls
so I applied this with following tweak.  Please take a look
at the result on testing branch of iio.git.

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index a427427aa324..5a863005aca6 100644
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -255,9 +255,8 @@ static int ad7768_reg_access(struct iio_dev *indio_dev,
        struct ad7768_state *st = iio_priv(indio_dev);
        int ret;
 
-       ret = iio_device_claim_direct_mode(indio_dev);
-       if (ret)
-               return ret;
+       if (!iio_device_claim_direct(indio_dev))
+               return -EBUSY;
 
        if (readval) {
                ret = ad7768_spi_reg_read(st, reg, 1);
@@ -269,7 +268,7 @@ static int ad7768_reg_access(struct iio_dev *indio_dev,
                ret = ad7768_spi_reg_write(st, reg, writeval);
        }
 err_release:
-       iio_device_release_direct_mode(indio_dev);
+       iio_device_release_direct(indio_dev);
 
        return ret;
 }


> ---
> v4 Changes:
> * None.
> 
> v3 Changes:
> * Also removed the mutex_init and lock variable.
> 
> v2 Changes:
> * New patch in v2. It replaces the guard(mutex) patch. 
> ---
>  drivers/iio/adc/ad7768-1.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index 2e2d50ccb744..f5509a0a36ab 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -154,7 +154,6 @@ static const struct iio_chan_spec ad7768_channels[] = {
>  struct ad7768_state {
>  	struct spi_device *spi;
>  	struct regulator *vref;
> -	struct mutex lock;
>  	struct clk *mclk;
>  	unsigned int mclk_freq;
>  	unsigned int samp_freq;
> @@ -256,18 +255,21 @@ static int ad7768_reg_access(struct iio_dev *indio_dev,
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> +	ret = iio_device_claim_direct_mode(indio_dev);
> +	if (ret)
> +		return ret;
> +
>  	if (readval) {
>  		ret = ad7768_spi_reg_read(st, reg, 1);
>  		if (ret < 0)
> -			goto err_unlock;
> +			goto err_release;
>  		*readval = ret;
>  		ret = 0;
>  	} else {
>  		ret = ad7768_spi_reg_write(st, reg, writeval);
>  	}
> -err_unlock:
> -	mutex_unlock(&st->lock);
> +err_release:
> +	iio_device_release_direct_mode(indio_dev);
>  
>  	return ret;
>  }
> @@ -471,18 +473,15 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> -
>  	ret = spi_read(st->spi, &st->data.scan.chan, 3);
>  	if (ret < 0)
> -		goto err_unlock;
> +		goto out;
>  
>  	iio_push_to_buffers_with_timestamp(indio_dev, &st->data.scan,
>  					   iio_get_time_ns(indio_dev));
>  
> -err_unlock:
> +out:
>  	iio_trigger_notify_done(indio_dev->trig);
> -	mutex_unlock(&st->lock);
>  
>  	return IRQ_HANDLED;
>  }
> @@ -611,8 +610,6 @@ static int ad7768_probe(struct spi_device *spi)
>  
>  	st->mclk_freq = clk_get_rate(st->mclk);
>  
> -	mutex_init(&st->lock);
> -
>  	indio_dev->channels = ad7768_channels;
>  	indio_dev->num_channels = ARRAY_SIZE(ad7768_channels);
>  	indio_dev->name = spi_get_device_id(spi)->name;