Re: [PATCH v4 3/4] iio: adc: ltc2378: Enable high-speed data capture

[Andy Shevchenko]

On Thu, Jun 25, 2026 at 11:35:40AM -0300, Marcelo Schmitt wrote:
> Make use of SPI transfer offloading to speed up data capture, enabling data
> acquisition at faster sample rates (up to 2 MSPS).

...

> +#include <linux/math.h>
> +#include <linux/math64.h>

The latter is superior, drop math.h

...

>  struct ltc2378_chip_info {
>  	const char *name;
>  	unsigned int internal_ref_uv;
>  	struct iio_chan_spec chan;
> +	struct iio_chan_spec offload_chan;
> +	unsigned int max_sample_rate_hz;

Perhaps _Hz for the consistency. I dunno in this case, because it's quite
widespread (in small letters).

> +	unsigned int tconv_ns;
>  };

...

> +		*val = st->cnv_Hz;

Ah, you already use that, so please do in the above.

...

> +	if (freq_Hz < 1 || freq_Hz > st->info->max_sample_rate_hz)

Can we use in_range()?

> +		return -ERANGE;

...

> +	do {
> +		cnv_wf.duty_length_ns = target;
> +		ret = pwm_round_waveform_might_sleep(st->cnv_trigger, &cnv_wf);
> +		if (ret)
> +			return ret;
> +		target += 10;  /* Increment by PWM duty cycle period */
> +	} while (count++ < 100 && cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS);

Seems count is not used directly, can be `while (--count ...)`  as usual pattern.

> +	/* Double check the minimum CNV high time is met */
> +	if (cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS)
> +		return -EIO;

Hmm... How is this IO issue?

> +	/*
> +	 * Configure SPI offload PWM trigger.
> +	 * The trigger should fire after tBUSYLH + tCONV + tDSDOBUSYL.
> +	 * Minimum time needed: TBUSYLH (13ns) + TCONV (part-specific) + TDSDOBUSYL (5ns)
> +	 *
> +	 * Use the same period as CNV PWM to avoid timing issues.
> +	 * Convert back from period to frequency for the SPI offload API.
> +	 */
> +	offload_period_ns = cnv_wf.period_length_ns;
> +	config->periodic.frequency_hz = DIV_ROUND_UP(HZ_PER_GHZ, offload_period_ns);
> +	min_read_offset = LTC2378_TBUSYLH_NS + st->info->tconv_ns + LTC2378_TDSDOBUSYL_NS;
> +	offload_offset_ns = min_read_offset;
> +	count = 0;
> +	do {
> +		config->periodic.offset_ns = offload_offset_ns;
> +		ret = spi_offload_trigger_validate(st->offload_trigger, config);
> +		if (ret)
> +			return ret;
> +		offload_offset_ns += 10;
> +	} while (count++ < 100 && config->periodic.offset_ns < min_read_offset);

Same comment against count.

-- 
With Best Regards,
Andy Shevchenko