netdev - Re: [PATCH net-next 6/6] net: dsa: sja1105: parse {rx,tx}-internal-delay-ps properties for RGMII delays

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Message-ID: <20211013172448.2db3b99b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 13 Oct 2021 17:24:48 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Prasanna Vengateshan <prasanna.vengateshan@...rochip.com>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>
Subject: Re: [PATCH net-next 6/6] net: dsa: sja1105: parse
 {rx,tx}-internal-delay-ps properties for RGMII delays

Some take it or leave it comments, checkpatch pointed out some extra
brackets so I had a look at the patch.

On Thu, 14 Oct 2021 01:23:13 +0300 Vladimir Oltean wrote:
> +	int rx_delay = -1, tx_delay = -1;
>  
> +	if (!phy_interface_mode_is_rgmii(phy_mode))
> +		return 0;
>  
> +	of_property_read_u32(port_dn, "rx-internal-delay-ps", &rx_delay);
> +	of_property_read_u32(port_dn, "tx-internal-delay-ps", &tx_delay);

If I'm reading this right you're depending on delays being left as -1
in case the property reads fail. Is this commonly accepted practice?
Why not code it up as:

	u32 rx_delay;

	if (of_property_read_u32(...))
		rx_delay = 0;
	else if (rx_delay != clamp(rx_delay, ...MIN, ...MAX)
		goto err;

or some such?

> +	if ((rx_delay && rx_delay < SJA1105_RGMII_DELAY_MIN_PS) ||
> +	    (tx_delay && tx_delay < SJA1105_RGMII_DELAY_MIN_PS) ||
> +	    (rx_delay > SJA1105_RGMII_DELAY_MAX_PS) ||
> +	    (tx_delay > SJA1105_RGMII_DELAY_MAX_PS)) {

nit: checkpatch says the brackets around the latter two are unnecessary,
     just in case it's not for symmetry / on purpose