netdev - Re: [PATCH v5 2/2] ethernet: eswin: Add eic7700 ethernet driver

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Message-ID: <aLlpUOr3IJzTuV1g@shell.armlinux.org.uk>
Date: Thu, 4 Sep 2025 11:26:24 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: weishangjuan@...incomputing.com
Cc: devicetree@...r.kernel.org, andrew+netdev@...n.ch, davem@...emloft.net,
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Subject: Re: [PATCH v5 2/2] ethernet: eswin: Add eic7700 ethernet driver

On Thu, Sep 04, 2025 at 05:01:25PM +0800, weishangjuan@...incomputing.com wrote:
> +struct eic7700_qos_priv {
> +	struct plat_stmmacenet_data *plat_dat;
> +	struct device *dev;
> +	struct regmap *hsp_regmap;
> +	u32 tx_delay_ps;
> +	u32 rx_delay_ps;
> +};
> +
> +/**
> + * eic7700_apply_delay - Apply TX or RX delay to a register value.
> + * @delay_ps: Delay in picoseconds, converted to 0.1ns units.
> + * @reg:      Pointer to register value to update in-place.
> + * @is_rx:    True for RX delay (bits 30:24), false for TX delay (bits 14:8).
> + *
> + * Converts delay from ps to 0.1ns units, capped by EIC7700_MAX_DELAY_UNIT.
> + * Updates only the RX or TX delay field (using FIELD_PREP), leaving all
> + * other bits in *@reg unchanged.
> + */
> +static void eic7700_apply_delay(u32 delay_ps, u32 *reg, bool is_rx)
> +{
> +	u32 val = min(delay_ps / 100, EIC7700_MAX_DELAY_UNIT);
> +
> +	if (is_rx) {
> +		*reg &= ~EIC7700_ETH_RX_ADJ_DELAY;
> +		*reg |= FIELD_PREP(EIC7700_ETH_RX_ADJ_DELAY, val);
> +	} else {
> +		*reg &= ~EIC7700_ETH_TX_ADJ_DELAY;
> +		*reg |= FIELD_PREP(EIC7700_ETH_TX_ADJ_DELAY, val);
> +	}
> +}

...

> +	/* Read rx-internal-delay-ps and update rx_clk delay */
> +	if (!of_property_read_u32(pdev->dev.of_node,
> +				  "rx-internal-delay-ps",
> +				  &dwc_priv->rx_delay_ps)) {
> +		eic7700_apply_delay(dwc_priv->rx_delay_ps,
> +				    &eth_dly_param, true);

I've been trying to figure out the reasoning behind the following:

1. the presence of dwc_priv->rx_delay_ps and dwc_priv->tx_delay_ps
   rather than just using a local variable ("delay" ?)
2. the presence of eic7700_apply_delay() when we have to do something
   different to get the delay value anyway

It seems to me that this should either be:

static void eic7700_parse_delay(u32 *reg, struct device *dev,
				const char *name, bool is_rx)
{
	u32 delay;

	if (of_property_read_u32(dev->of_node, name, &delay)) {
		dev_warn(dev, "can't get %s\n", name);
		return
	}

	if (is_rx) {
		*reg &= ~EIC7700_ETH_RX_ADJ_DELAY;
		*reg |= FIELD_PREP(EIC7700_ETH_RX_ADJ_DELAY, delay);
	} else {
		*reg &= ~EIC7700_ETH_TX_ADJ_DELAY;
		*reg |= FIELD_PREP(EIC7700_ETH_TX_ADJ_DELAY, delay);
	}
}

or just not bother with the function at all and just write it out
fully in the probe function.

Thanks.

-- 
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