linux-kernel - Re: [PATCH v5 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

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Message-ID: <c1d21e3c-b0a3-40a5-b693-a38673f8bf53@gmail.com>
Date: Tue, 16 Sep 2025 07:52:07 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Jonathan Cameron <jic23@...nel.org>,
 Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: 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>, Linus Walleij
 <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v5 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

On 15/09/2025 23:13, Jonathan Cameron wrote:
> On Mon, 15 Sep 2025 17:12:34 +0300
> Andy Shevchenko <andriy.shevchenko@...el.com> wrote:
> 
>> On Mon, Sep 15, 2025 at 10:12:43AM +0300, Matti Vaittinen wrote:
>>> The ROHM BD79112 is an ADC/GPIO with 32 channels. The channel inputs can
>>> be used as ADC or GPIO. Using the GPIOs as IRQ sources isn't supported.
>>>
>>> The ADC is 12-bit, supporting input voltages up to 5.7V, and separate I/O
>>> voltage supply. Maximum SPI clock rate is 20 MHz (10 MHz with
>>> daisy-chain configuration) and maximum sampling rate is 1MSPS.
>>>
>>> The IC does also support CRC but it is not implemented in the driver.
>>
>> ...
>>
>>> +static int bd79112_probe(struct spi_device *spi)
>>> +{
>>> +	struct bd79112_data *data;
>>> +	struct iio_dev *iio_dev;
>>> +	struct iio_chan_spec *cs;
>>> +	struct device *dev = &spi->dev;
>>> +	unsigned long gpio_pins, pin;
>>> +	unsigned int i;
>>> +	int ret;
>>> +
>>> +	iio_dev = devm_iio_device_alloc(dev, sizeof(*data));
>>> +	if (!iio_dev)
>>> +		return -ENOMEM;
>>> +
>>> +	data = iio_priv(iio_dev);
>>> +	data->spi = spi;
>>> +	data->dev = dev;
>>> +	data->map = devm_regmap_init(dev, NULL, data, &bd79112_regmap);
>>> +	if (IS_ERR(data->map))
>>> +		return dev_err_probe(dev, PTR_ERR(data->map),
>>> +				     "Failed to initialize Regmap\n");
>>> +
>>> +	ret = devm_regulator_get_enable_read_voltage(dev, "vdd");
>>> +	if (ret < 0)
>>> +		return dev_err_probe(dev, ret, "Failed to get the Vdd\n");
>>
>>> +	data->vref_mv = ret / 1000;
>>
>> I still think moving to _mV is the right thing to do.
>> There is no 'mv' in the physics for Volts.
> 
> I'm not disagreeing with this review but I'm also not going to hold a
> driver back for that given timing is pretty much such that I merge it
> today or it sits a cycle and this one is very near...
> I'll get fussier on this once we have written up some guidance and may
> well send a patch to modify existing recent cases like this one!

As I replied to Andy, I am disagreeing with this. I hope we won't start 
renaming variables with capital letters :(

>>
>>> +	ret = devm_regulator_get_enable(dev, "iovdd");
>>> +	if (ret < 0)
>>> +		return dev_err_probe(dev, ret, "Failed to enable I/O voltage\n");
>>> +
>>> +	data->read_xfer[0].tx_buf = &data->read_tx[0];
>>> +	data->read_xfer[0].len = sizeof(data->read_tx);
>>> +	data->read_xfer[0].cs_change = 1;
>>> +	data->read_xfer[1].rx_buf = &data->read_rx;
>>> +	data->read_xfer[1].len = sizeof(data->read_rx);
>>> +	spi_message_init_with_transfers(&data->read_msg, data->read_xfer, 2);
>>
>>> +	devm_spi_optimize_message(dev, spi, &data->read_msg);
>>
>> And if it fails?..
> I've added the following and applied the series.

Thanks!

> Note I'm cutting this fine so if we get any build issues or similar
> it might well get pushed back to next cycle yet!
> 
> diff --git a/drivers/iio/adc/rohm-bd79112.c b/drivers/iio/adc/rohm-bd79112.c
> index b406d4ee5411..d15e06c8b94d 100644
> --- a/drivers/iio/adc/rohm-bd79112.c
> +++ b/drivers/iio/adc/rohm-bd79112.c
> @@ -454,12 +454,18 @@ static int bd79112_probe(struct spi_device *spi)
>          data->read_xfer[1].rx_buf = &data->read_rx;
>          data->read_xfer[1].len = sizeof(data->read_rx);
>          spi_message_init_with_transfers(&data->read_msg, data->read_xfer, 2);
> -       devm_spi_optimize_message(dev, spi, &data->read_msg);
> +       ret = devm_spi_optimize_message(dev, spi, &data->read_msg);
> +       if (ret < 0)
> +               return dev_err_probe(dev, ret,
> +                                    "Failed to optimize SPI read message\n");
>   

I am not really sure under what conditions the 
devm_spi_optimize_message() could fail. It might be enough to print a 
warning and proceed, but I don't think returning is a problem either.

Thanks a lot for going an extra mile and taking care of this!

Yours,
	-- Matti