linux-kernel - Re: [PATCH net-next 4/5] dpll: zl3073x: Add support to adjust phase

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Message-ID: <495a37e7-e31d-4671-a4d9-7e653ad80b60@redhat.com>
Date: Tue, 15 Jul 2025 15:12:01 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Ivan Vecera <ivecera@...hat.com>, netdev@...r.kernel.org
Cc: Prathosh Satish <Prathosh.Satish@...rochip.com>,
 Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
 Jiri Pirko <jiri@...nulli.us>, "David S. Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
 Michal Schmidt <mschmidt@...hat.com>, Petr Oros <poros@...hat.com>
Subject: Re: [PATCH net-next 4/5] dpll: zl3073x: Add support to adjust phase

On 7/10/25 5:38 PM, Ivan Vecera wrote:
> +static int
> +zl3073x_dpll_output_pin_phase_adjust_get(const struct dpll_pin *dpll_pin,
> +					 void *pin_priv,
> +					 const struct dpll_device *dpll,
> +					 void *dpll_priv,
> +					 s32 *phase_adjust,
> +					 struct netlink_ext_ack *extack)
> +{
> +	struct zl3073x_dpll *zldpll = dpll_priv;
> +	struct zl3073x_dev *zldev = zldpll->dev;
> +	struct zl3073x_dpll_pin *pin = pin_priv;
> +	u32 synth_freq;
> +	s32 phase_comp;
> +	u8 out, synth;
> +	int rc;
> +
> +	out = zl3073x_output_pin_out_get(pin->id);
> +	synth = zl3073x_out_synth_get(zldev, out);
> +	synth_freq = zl3073x_synth_freq_get(zldev, synth);
> +
> +	guard(mutex)(&zldev->multiop_lock);
> +
> +	/* Read output configuration */
> +	rc = zl3073x_mb_op(zldev, ZL_REG_OUTPUT_MB_SEM, ZL_OUTPUT_MB_SEM_RD,
> +			   ZL_REG_OUTPUT_MB_MASK, BIT(out));
> +	if (rc)
> +		return rc;
> +
> +	/* Read current output phase compensation */
> +	rc = zl3073x_read_u32(zldev, ZL_REG_OUTPUT_PHASE_COMP, &phase_comp);
> +	if (rc)
> +		return rc;
> +
> +	/* Value in register is expressed in half synth clock cycles */
> +	phase_comp *= (int)div_u64(PSEC_PER_SEC, 2 * synth_freq);

Is 'synth_freq' guaranteed to be != 0 even on extreme conditions?
Possibly a comment or an explicit check could help.

/P