linux-kernel - Re: [PATCH 06/15] spi: spi-offload-trigger-pwm: Use duty offset

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Message-ID: <a94fe92c-ec2e-42d9-9a88-f40f243560ca@baylibre.com>
Date: Sat, 30 Aug 2025 11:41:25 -0500
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-spi@...r.kernel.org,
 Uwe Kleine-König <ukleinek@...libre.com>
Cc: Axel Haslam <ahaslam@...libre.com>, jic23@...nel.org,
 Michael.Hennerich@...log.com, nuno.sa@...log.com, eblanc@...libre.com,
 andy@...nel.org, corbet@....net, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, broonie@...nel.org, Jonathan.Cameron@...wei.com,
 andriy.shevchenko@...ux.intel.com, marcelo.schmitt1@...il.com
Subject: Re: [PATCH 06/15] spi: spi-offload-trigger-pwm: Use duty offset

On 8/29/25 7:42 PM, Marcelo Schmitt wrote:
> From: Axel Haslam <ahaslam@...libre.com>
> 
> Pass the duty offset to the waveform pwm.
> 
> Signed-off-by: Axel Haslam <ahaslam@...libre.com>
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> ---
>  drivers/spi/spi-offload-trigger-pwm.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/spi-offload-trigger-pwm.c b/drivers/spi/spi-offload-trigger-pwm.c
> index 805ed41560df..8413aeb3689d 100644
> --- a/drivers/spi/spi-offload-trigger-pwm.c
> +++ b/drivers/spi/spi-offload-trigger-pwm.c
> @@ -51,13 +51,13 @@ static int spi_offload_trigger_pwm_validate(struct spi_offload_trigger *trigger,
>  	wf.period_length_ns = DIV_ROUND_UP_ULL(NSEC_PER_SEC, periodic->frequency_hz);
>  	/* REVISIT: 50% duty-cycle for now - may add config parameter later */
>  	wf.duty_length_ns = wf.period_length_ns / 2;
> -
> +	wf.duty_offset_ns = periodic->offset_ns;

I would be tempted to put the loop check here:

	offload_offset_ns = periodic->offset_ns;

	do {
		wf.offset_ns = offload_offset_ns;
		ret = pwm_round_waveform_might_sleep(st->pwm, &wf);
		if (ret)
			return ret;
		offload_offset_ns += 10;

	} while (wf.offset_ns < periodic->offset_ns);

	wf.duty_offset_ns = periodic->offset_ns;

instead of in the ADC driver so that all future callers don't have to
repeat this.

Also cc: Uwe in case he has any better suggestions on how to avoid
repeating such verbose validations by all uses of the PWM waveform
APIs.


>  	ret = pwm_round_waveform_might_sleep(st->pwm, &wf);
>  	if (ret < 0)
>  		return ret;
>  
>  	periodic->frequency_hz = DIV_ROUND_UP_ULL(NSEC_PER_SEC, wf.period_length_ns);
> -
> +	periodic->offset_ns = wf.duty_offset_ns;
>  	return 0;
>  }
>  
> @@ -77,6 +77,7 @@ static int spi_offload_trigger_pwm_enable(struct spi_offload_trigger *trigger,
>  	wf.period_length_ns = DIV_ROUND_UP_ULL(NSEC_PER_SEC, periodic->frequency_hz);
>  	/* REVISIT: 50% duty-cycle for now - may add config parameter later */
>  	wf.duty_length_ns = wf.period_length_ns / 2;
> +	wf.duty_offset_ns = periodic->offset_ns;
>  
>  	return pwm_set_waveform_might_sleep(st->pwm, &wf, false);
>  }