netdev - Re: [RFC PATCH net-next 6/8] net: dsa: mt7530: simplify mt7530_setup

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Message-ID: <20240115213720.vxlumsjwrjdkqxsl@skbuf>
Date: Mon, 15 Jan 2024 23:37:20 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Arınç ÜNAL <arinc.unal@...nc9.com>
Cc: Daniel Golle <daniel@...rotopia.org>,
	Landen Chao <Landen.Chao@...iatek.com>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
	Luiz Angelo Daros de Luca <luizluca@...il.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [RFC PATCH net-next 6/8] net: dsa: mt7530: simplify
 mt7530_setup_port6() and change to void

On Sat, Jan 13, 2024 at 01:25:27PM +0300, Arınç ÜNAL wrote:
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index 3ce4e0bb04dd..3a02308763ca 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -414,72 +414,56 @@ mt753x_preferred_default_local_cpu_port(struct dsa_switch *ds)
>  }
>  
>  /* Setup port 6 interface mode and TRGMII TX circuit */
> -static int
> +static void
>  mt7530_setup_port6(struct dsa_switch *ds, phy_interface_t interface)
>  {
>  	struct mt7530_priv *priv = ds->priv;
> -	u32 ncpo1, ssc_delta, trgint, xtal;
> +	u32 ncpo1, ssc_delta, xtal;
>  
>  	mt7530_clear(priv, MT7530_MHWTRAP, MHWTRAP_P6_DIS);
>  
> +	if (interface == PHY_INTERFACE_MODE_RGMII)
> +		return;

It would be good to add a comment here which states that the port comes
out of reset with values good for RGMII.

Also, there's a built-in assumption in this patch, that dynamically
switching between RGMII and TRGMII is not possible. This is because
phylink mac_config() is not necesarily called only once immediately
after reset, but after each major_config().

The fact that the driver sets both PHY_INTERFACE_MODE_RGMII and
PHY_INTERFACE_MODE_TRGMII at once in config->supported_interfaces does
not disprove that dynamic reconfiguration is possible. Normally,
interfaces for which it doesn't make sense to dynamically reconfigure
(they are wired to fixed pinout) have a single bit set in
supported_interfaces. Is this switching something that makes any sense
at all, given that port 6 is internal? It's not something that phylink
knows to do today, but if this is theoretically possible and remotely
useful, someone might end up wanting, in the future, to revert this patch.