linux-kernel - Re: [PATCH v5 07/11] iio: adc: ad4170: Add clock provider support

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Message-ID: <656c43dd-c39d-4e35-a9d8-70383c0836a0@baylibre.com>
Date: Mon, 16 Jun 2025 16:11:29 -0500
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: jic23@...nel.org, lars@...afoo.de, Michael.Hennerich@...log.com,
 nuno.sa@...log.com, andy@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, linus.walleij@...aro.org, brgl@...ev.pl,
 marcelo.schmitt1@...il.com
Subject: Re: [PATCH v5 07/11] iio: adc: ad4170: Add clock provider support

On 6/10/25 3:33 PM, Marcelo Schmitt wrote:
> The AD4170 chip can use an externally supplied clock at the XTAL2 pin, or
> an external crystal connected to the XTAL1 and XTAL2 pins. Alternatively,
> the AD4170 can provide its 16 MHz internal clock at the XTAL2 pin. In
> addition, the chip has a programmable clock divider that allows dividing
> the external or internal clock frequency, however, control for that is not
> provided in this patch. Extend the AD4170 driver so it effectively uses the
> provided external clock, if any, or supplies its own clock as a clock
> provider.
> 

...

> +static int ad4170_clock_select(struct iio_dev *indio_dev)
> +{
> +	struct ad4170_state *st = iio_priv(indio_dev);
> +	struct device *dev = &st->spi->dev;
> +	struct clk *ext_clk;
> +	int ret;
> +
> +	ext_clk = devm_clk_get_optional_enabled(dev, NULL);
> +	if (IS_ERR(ext_clk))
> +		return dev_err_probe(dev, PTR_ERR(ext_clk),
> +				     "Failed to get external clock\n");
> +
> +	if (!ext_clk) {
> +		/* Use internal clock reference */
> +		st->mclk_hz = AD4170_INT_CLOCK_16MHZ;
> +		st->clock_ctrl |= FIELD_PREP(AD4170_CLOCK_CTRL_CLOCKSEL_MSK,
> +					     AD4170_CLOCK_CTRL_CLOCKSEL_INT_OUT);
> +
> +		if (!device_property_read_bool(&st->spi->dev, "#clock-cells"))

This isn't a flag, so device_property_present() is probably more correct.

> +			return 0;
> +
> +		return ad4170_register_clk_provider(indio_dev);
> +	}
> +
> +	/* Read optional clock-names prop to specify the external clock type */
> +	ret = device_property_match_property_string(dev, "clock-names",
> +						    ad4170_clk_sel,
> +						    ARRAY_SIZE(ad4170_clk_sel));
> +
> +	ret = ret < 0 ? 0 : ret; /* Default to external clock if no clock-names */
> +	st->clock_ctrl |= FIELD_PREP(AD4170_CLOCK_CTRL_CLOCKSEL_MSK,
> +				     AD4170_CLOCK_CTRL_CLOCKSEL_EXT + ret);
> +
> +	st->mclk_hz = clk_get_rate(ext_clk);
> +	if (st->mclk_hz < AD4170_EXT_CLOCK_MHZ_MIN ||
> +	    st->mclk_hz > AD4170_EXT_CLOCK_MHZ_MAX) {
> +		return dev_err_probe(dev, -EINVAL,
> +				     "Invalid external clock frequency %u\n",
> +				     st->mclk_hz);
> +	}
> +
> +	return 0;
> +}