linux-kernel - Re: [PATCH v2 10/10] iio: adc: ad7606: Disable PWM usage for non backend version

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Message-ID: <20240929135603.0ceb6cfc@jic23-huawei>
Date: Sun, 29 Sep 2024 13:56:03 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Guillaume Stols <gstols@...libre.com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>, Lars-Peter
 Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Jonathan Corbet <corbet@....net>, Michal Marek
 <mmarek@...e.com>, linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fbdev@...r.kernel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
 aardelean@...libre.com, dlechner@...libre.com, jstephan@...libre.com
Subject: Re: [PATCH v2 10/10] iio: adc: ad7606: Disable PWM usage for non
 backend version

On Fri, 20 Sep 2024 17:33:30 +0000
Guillaume Stols <gstols@...libre.com> wrote:

> Since the pwm was introduced before backend, there was an example use
> whit triggered buffers. However, using it may be dangerous, because if
> the PWM goes too fast, a new conversion can be triggered before the
> transmission is over, whit the associated mess in the buffers.
> Until a solution is found to mitigate this risk, for instante CRC
> support, the PWM will be disabled.
> 
> Signed-off-by: Guillaume Stols <gstols@...libre.com>

Whilst I can see the logic introducing it in two steps, maybe
shout a bit more about that in the original patch as otherwise
some foolish unnamed maintainer might pick up part of this series
leaving things in a bad state for a kernel release.

The earlier patch 'recommends' it isn't used which is a bit week.
Say support is going to be removed later.
> ---
>  drivers/iio/adc/ad7606.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7606.c b/drivers/iio/adc/ad7606.c
> index f710445bdc22..0c12ca237ee9 100644
> --- a/drivers/iio/adc/ad7606.c
> +++ b/drivers/iio/adc/ad7606.c
> @@ -599,7 +599,6 @@ static int ad7606_buffer_postenable(struct iio_dev *indio_dev)
>  	struct ad7606_state *st = iio_priv(indio_dev);
>  
>  	gpiod_set_value(st->gpio_convst, 1);
> -	ad7606_pwm_set_swing(st);
>  
>  	return 0;
>  }
> @@ -609,7 +608,6 @@ static int ad7606_buffer_predisable(struct iio_dev *indio_dev)
>  	struct ad7606_state *st = iio_priv(indio_dev);
>  
>  	gpiod_set_value(st->gpio_convst, 0);
> -	ad7606_pwm_set_low(st);
>  
>  	return 0;
>  }
> @@ -838,6 +836,12 @@ int ad7606_probe(struct device *dev, int irq, void __iomem *base_address,
>  		indio_dev->setup_ops = &ad7606_pwm_buffer_ops;
>  	} else {
>  		init_completion(&st->completion);
> +
> +		/* Reserve the PWM use only for backend (force gpio_convst definition) */
> +		if (!st->gpio_convst)
> +			return dev_err_probe(dev, -EINVAL,
> +					     "No backend, connect convst to a GPIO");
> +
>  		ret = devm_request_threaded_irq(dev, irq,
>  						NULL,
>  						&ad7606_interrupt,
>