linux-kernel - Re: [PATCH v2 09/10] iio: adc: ad7476: Support ROHM BD79105

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Message-ID: <CAHp75VfBvqzKR53qTbiGxE-JQdLOuA3+M-Z=9S6LTf0fGnwmvg@mail.gmail.com>
Date: Thu, 7 Aug 2025 23:28:27 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>, Lars-Peter Clausen <lars@...afoo.de>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	David Lechner <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/10] iio: adc: ad7476: Support ROHM BD79105

On Thu, Aug 7, 2025 at 11:35 AM Matti Vaittinen
<mazziesaccount@...il.com> wrote:
>
> The ROHM BD79105 is a simple 16-bit ADC accessible via SPI*.
>
> The BD79105 has a CONVSTART pin, which must be set high to start the ADC
> conversion. Unlike with the ad7091 and ad7091r which also have a
> CONVSTART pin, the BD79105 requires that the pin must remain high also
> for the duration of the SPI access.
>
> (*) Couple of words about the SPI. The BD79105 has pins named as
> CONVSTART, SCLK, DIN and DOUT. For the curious reader, DIN is not SPI
> ISO.
>
> DIN is a signal which can be used as a chip-select. When DIN is pulled
> low, the ADC will output the completed measurement via DOUT as SCLK is
> clocked. According to the data-sheet, the DIN can also be used for
> daisy-chaining multiple ADCs. Furthermore, DOUT can be used also for a
> 'data-ready' -IRQ. These modes aren't supported by this driver.
>
> Support reading ADC scale and data from the BD79105 using SPI, when DIN
> is used as a chip-select.

...

> +static void bd79105_convst_enable(struct ad7476_state *st)
> +{
> +       if (!st->convst_gpio)
> +               return;

Still consider this unneeded churn. 3us delay is tolerable in almost
any setup with this driver.

> +       gpiod_set_value(st->convst_gpio, 1);
> +       /* Worst case, 2790 nS required for conversion */

nS --> ns (SI unit for seconds is 's')

> +       ndelay(2790);
> +}

...

> +       /*
> +        * The BD79105 starts ADC data conversion when the CONVSTART line is
> +        * set HIGH. The CONVSTART must be kept HIGH until the data has been
> +        * read from the ADC.

Is this terminology in absolute levels of the pin or logical ones
(that implied active-low)? If it's the latter, use active/inactive
instead as the GPIO subsystem does.

> +        */

-- 
With Best Regards,
Andy Shevchenko