linux-kernel - Re: [PATCH 7/8] iio: adc: ad7476: Support ROHM BD79105

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Message-ID: <f738f3fb-2ce8-4699-bb13-3778ed1c6606@gmail.com>
Date: Thu, 7 Aug 2025 10:30:57 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.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 7/8] iio: adc: ad7476: Support ROHM BD79105

On 06/08/2025 23:26, Andy Shevchenko wrote:
> On Wed, Aug 06, 2025 at 10:04:43AM +0300, Matti Vaittinen 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. Also, 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;
> 
> With 10ns sleep in mind this is also unneeded check.
> 
>> +	gpiod_set_value(st->convst_gpio, 1);
> 
>> +	udelay(1); /* 10ns required for conversion */
> 
> We have ndelay(). But I believe toggling GPIO is much longer operation.

Thanks for the review Andy.

As I replied to David, this 10nS is rubbish. I need to clarify the right 
value.


Yours,
	-- Matti