netdev - Re: [PATCH net-next v11 13/14] dpll: zl3073x: Add support to get/set frequency on input pins

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Message-ID: <72bab3b2-bdd6-43f6-9243-55009f9c1071@redhat.com>
Date: Thu, 19 Jun 2025 13:15:23 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Ivan Vecera <ivecera@...hat.com>, netdev@...r.kernel.org
Cc: Prathosh Satish <Prathosh.Satish@...rochip.com>,
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
 Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
 Jiri Pirko <jiri@...nulli.us>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
 Jason Gunthorpe <jgg@...pe.ca>, Shannon Nelson <shannon.nelson@....com>,
 Dave Jiang <dave.jiang@...el.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 Michal Schmidt <mschmidt@...hat.com>, Petr Oros <poros@...hat.com>
Subject: Re: [PATCH net-next v11 13/14] dpll: zl3073x: Add support to get/set
 frequency on input pins

On 6/16/25 10:14 PM, Ivan Vecera wrote:
> +/**
> + * zl3073x_dpll_input_ref_frequency_get - get input reference frequency
> + * @zldpll: pointer to zl3073x_dpll
> + * @ref_id: reference id
> + * @frequency: pointer to variable to store frequency
> + *
> + * Reads frequency of given input reference.
> + *
> + * Return: 0 on success, <0 on error
> + */
> +static int
> +zl3073x_dpll_input_ref_frequency_get(struct zl3073x_dpll *zldpll, u8 ref_id,
> +				     u32 *frequency)
> +{
> +	struct zl3073x_dev *zldev = zldpll->dev;
> +	u16 base, mult, num, denom;
> +	int rc;
> +
> +	guard(mutex)(&zldev->multiop_lock);
> +
> +	/* Read reference configuration */
> +	rc = zl3073x_mb_op(zldev, ZL_REG_REF_MB_SEM, ZL_REF_MB_SEM_RD,
> +			   ZL_REG_REF_MB_MASK, BIT(ref_id));
> +	if (rc)
> +		return rc;
> +
> +	/* Read registers to compute resulting frequency */
> +	rc = zl3073x_read_u16(zldev, ZL_REG_REF_FREQ_BASE, &base);
> +	if (rc)
> +		return rc;
> +	rc = zl3073x_read_u16(zldev, ZL_REG_REF_FREQ_MULT, &mult);
> +	if (rc)
> +		return rc;
> +	rc = zl3073x_read_u16(zldev, ZL_REG_REF_RATIO_M, &num);
> +	if (rc)
> +		return rc;
> +	rc = zl3073x_read_u16(zldev, ZL_REG_REF_RATIO_N, &denom);
> +	if (rc)
> +		return rc;
> +
> +	/* Sanity check that HW has not returned zero denominator */
> +	if (!denom) {
> +		dev_err(zldev->dev,
> +			"Zero divisor for ref %u frequency got from device\n",
> +			ref_id);
> +		return -EINVAL;
> +	}
> +
> +	/* Compute the frequency */
> +	*frequency = base * mult * num / denom;

As base, mult, num and denom are u16, the above looks like integer
overflow prone.

I think you should explicitly cast to u64, and possibly use a u64 frequency.

/P