linux-kernel - Re: [PATCH v3 7/9] iio: imu: adis

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Date: Tue, 21 May 2024 12:56:43 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Ramona Gradinariu <ramona.bolboaca13@...il.com>, 
	linux-kernel@...r.kernel.org, jic23@...nel.org, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, conor+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, robh@...nel.org, nuno.sa@...log.com
Subject: Re: [PATCH v3 7/9] iio: imu: adis_trigger: Allow level interrupts

On Fri, 2024-05-17 at 10:47 +0300, Ramona Gradinariu wrote:
> Currently, adis library allows configuration only for edge interrupts,
> needed for data ready sampling.
> This patch removes the restriction for level interrupts, which are
> needed to handle FIFO watermark interrupts.
> Furthermore, in case of level interrupts, devm_request_threaded_irq is
> used for interrupt allocation, to avoid blocking the processor while
> retrieving the FIFO samples.

Technically this not totally accurate (though ends up being true) as we do read
the FIFO samples in a thread already. The part that runs on the top halve should
be:

iio_trigger_generic_data_rdy_poll() -> iio_trigger_poll() -> iio_pollfunc_store_time()

and given the FIFO nature (as the interrupt keeps firing until FIFO_CNT drops
below the watermark), it seems this is enough for you to see some freezes.

Anyhow, I'd say the commit message should be a bit refactored. This also leads to
another minor detail/question (see below)

> 
> Signed-off-by: Ramona Gradinariu <ramona.bolboaca13@...il.com>
> ---
> changes in v3:
>  - new patch
>  drivers/iio/imu/adis_trigger.c | 39 ++++++++++++++++++----------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/iio/imu/adis_trigger.c b/drivers/iio/imu/adis_trigger.c
> index f890bf842db8..becf1f558b4e 100644
> --- a/drivers/iio/imu/adis_trigger.c
> +++ b/drivers/iio/imu/adis_trigger.c
> @@ -34,21 +34,16 @@ static int adis_validate_irq_flag(struct adis *adis)
>  	if (adis->data->unmasked_drdy)
>  		adis->irq_flag |= IRQF_NO_AUTOEN;
>  	/*
> -	 * Typically this devices have data ready either on the rising edge
> or
> -	 * on the falling edge of the data ready pin. This checks enforces
> that
> -	 * one of those is set in the drivers... It defaults to
> -	 * IRQF_TRIGGER_RISING for backward compatibility with devices that
> -	 * don't support changing the pin polarity.
> +	 * Typically adis devices without fifo have data ready either on the
> +	 * rising edge or on the falling edge of the data ready pin.
> +	 * IMU devices with fifo support have the watermark pin level driven
> +	 * either high or low when the fifo is filled with the desired number
> +	 * of samples.
> +	 * It defaults to IRQF_TRIGGER_RISING for backward compatibility with
> +	 * devices that don't support changing the pin polarity.
>  	 */
> -	if (direction == IRQF_TRIGGER_NONE) {
> +	if (direction == IRQF_TRIGGER_NONE)
>  		adis->irq_flag |= IRQF_TRIGGER_RISING;
> -		return 0;
> -	} else if (direction != IRQF_TRIGGER_RISING &&
> -		   direction != IRQF_TRIGGER_FALLING) {
> -		dev_err(&adis->spi->dev, "Invalid IRQ mask: %08lx\n",
> -			adis->irq_flag);
> -		return -EINVAL;
> -	}

I guess then we should rename the function as no actual validation is being
done, right?

> 
>  	return 0;
>  }
> @@ -77,11 +72,19 @@ int devm_adis_probe_trigger(struct adis *adis, struct
> iio_dev *indio_dev)
>  	if (ret)
>  		return ret;
> 
> -	ret = devm_request_irq(&adis->spi->dev, adis->spi->irq,
> -			       &iio_trigger_generic_data_rdy_poll,
> -			       adis->irq_flag,
> -			       indio_dev->name,
> -			       adis->trig);
> +	if (adis->irq_flag & (IRQF_TRIGGER_HIGH | IRQF_TRIGGER_LOW))
> +		ret = devm_request_threaded_irq(&adis->spi->dev, adis->spi-
> >irq,
> +						NULL,
> +						&iio_trigger_generic_data_rdy
> _poll,
> +						adis->irq_flag |
> IRQF_ONESHOT,
> +						indio_dev->name,
> +						adis->trig);

So, this is not really a big deal for me but I wonder if we should actually tie
this change to the device having FIFO support (so a boolean in the adis_data
struct)? It seems to me that's the real reason for the split... With the
boolean, we could also constrain the IRQ level support for devices supporting
FIFOs. Anyhow, since this is the first supported device with a FIFO having the
boolean (while it makes sense to me) may add more overhead than needed to the
series so I'm fine with this as-is.

- Nuno Sá
>