linux-kernel - Re: [PATCH v1 08/15] iio: adc: ad7768-1: use guard(mutex) to simplify code

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Message-ID: <3de36de0-93ee-4ef3-a4a9-7a8f187eb4d8@baylibre.com>
Date: Tue, 7 Jan 2025 17:42:11 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 marcelo.schmitt1@...il.com
Subject: Re: [PATCH v1 08/15] iio: adc: ad7768-1: use guard(mutex) to simplify
 code

On 1/7/25 9:25 AM, Jonathan Santos wrote:
> Use guard(mutex) from cleanup.h to remove most of the gotos and to make
> the code simpler and less likely to fail due to forgetting to unlock
> the resources.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---

...

> @@ -484,7 +477,7 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> +	guard(mutex)(&st->lock);
>  
>  	ret = spi_read(st->spi, &st->data.scan.chan, 3);
>  	if (ret < 0)
> @@ -495,7 +488,6 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
>  
>  err_unlock:

nit: also rename the label since it is no longer unlocking

>  	iio_trigger_notify_done(indio_dev->trig);
> -	mutex_unlock(&st->lock);
>  
>  	return IRQ_HANDLED;
>  }

I'm also wondering if we should just drop this lock. It is only protecting
a triggered buffer SPI xfer and debugfs register access from happening at the
same time.

Since we have to write a magic value to exit conversion mode, reading registers
during a buffered read is going to cause problems anyway. So we could just
remove the mutex lock and use iio_device_claim_direct_mode() instead in
ad7768_reg_access().