linux-kernel - Re: [PATCH 2/2] iio: frequency: Add ADF4382

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Message-ID: <b56089e4-ee82-4685-9da8-69cfb6471ec0@gmail.com>
Date: Thu, 14 Nov 2024 14:27:46 +0100
From: Javier Carrasco <javier.carrasco.cruz@...il.com>
To: Ciprian Hegbeli <ciprian.hegbeli@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Kim Seer Paller <kimseer.paller@...log.com>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: frequency: Add ADF4382

On 14/11/2024 14:03, Ciprian Hegbeli wrote:
> The ADF4382A is a high performance, ultralow jitter, Frac-N PLL
> with integrated VCO ideally suited for LO generation for 5G applications
> or data converter clock applications. The high performance
> PLL has a figure of merit of -239 dBc/Hz, low 1/f Noise and
> high PFD frequency of 625MHz in integer mode that can achieve
> ultralow in-band noise and integrated jitter. The ADF4382A can
> generate frequencies in a fundamental octave range of 11.5 GHz to
> 21 GHz, thereby eliminating the need for sub-harmonic filters. The
> divide by 2 and 4 output dividers on the part allow frequencies to
> be generated from 5.75GHz to 10.5GHz and 2.875GHz to 5.25GHz
> respectively.
> 
> Signed-off-by: Ciprian Hegbeli <ciprian.hegbeli@...log.com>
> ---
>  drivers/iio/frequency/Kconfig   |   11 +
>  drivers/iio/frequency/Makefile  |    1 +
>  drivers/iio/frequency/adf4382.c | 1825 +++++++++++++++++++++++++++++++
>  3 files changed, 1837 insertions(+)
>  create mode 100644 drivers/iio/frequency/adf4382.c

...

> +static int _adf4382_set_freq(struct adf4382_state *st)
> +{
> +	u32 frac2_word = 0;
> +	u32 mod2_word = 0;
> +	u64 pfd_freq_hz;
> +	u32 frac1_word;
> +	u8 clkout_div;
> +	u32 read_val;
> +	u8 dclk_div1;
> +	u8 int_mode;
> +	u8 en_bleed;
> +	u8 ldwin_pw;
> +	u16 n_int;
> +	u8 div1;
> +	u64 tmp;
> +	u64 vco;
> +	int ret;
> +	u8 var;
> +
> +	ret = adf4382_pfd_compute(st, &pfd_freq_hz);
> +	if (ret) {
> +		dev_err(&st->spi->dev, "PFD frequency is out of range.\n");
> +		return ret;
> +	}
> +
> +	for (clkout_div = 0; clkout_div <= st->clkout_div_reg_val_max; clkout_div++) {
> +		tmp =  (1 << clkout_div) * st->freq;
> +		if (tmp < st->vco_min || tmp > st->vco_max)
> +			continue;
> +
> +		vco = tmp;
> +		break;
> +	}
> +

(At least) LLVM/Clang complains about vco for a good reason: you may use
it without proper initialization if the for loop does not assign any
value. I guess you meant it to be initialized to zero in the declaration.

> +	if (vco == 0) {
> +		dev_err(&st->spi->dev, "Output frequency is out of range.\n");
> +		ret = -EINVAL;
> +		return ret;
> +	}
> +

Best regards,
Javier Carrasco