Subject: Re: [PATCH net-next 1/6] net: dsa: vsc73xx: convert to PHYLINK

From: "Russell King (Oracle)" <[email-masked]>
Date: Thu, 22 Jun 2023 12:55:52 +0100

On Wed, Jun 21, 2023 at 09:12:56PM +0200, Pawel Dembicki wrote:
> +	/* This driver does not make use of the speed, duplex, pause or the
> +	 * advertisement in its mac_config, so it is safe to mark this driver
> +	 * as non-legacy.
> +	 */
> +	config->legacy_pre_march2020 = false;

Great stuff, thanks!

> +static void vsc73xx_phylink_mac_config(struct dsa_switch *ds, int port,
> +				       unsigned int mode,
> +				       const struct phylink_link_state *state)
> +{
> +	struct vsc73xx *vsc = ds->priv;

Nit: normally have a blank line between function variable declarations
and the rest of the function body.

>  	/* Special handling of the CPU-facing port */
>  	if (port == CPU_PORT) {
>  		/* Other ports are already initialized but not this one */
> @@ -775,104 +803,92 @@ static void vsc73xx_adjust_link(struct dsa_switch *ds, int port,
>  			      VSC73XX_ADVPORTM_ENA_GTX |
>  			      VSC73XX_ADVPORTM_DDR_MODE);
>  	}
> +}
>  
> -	/* This is the MAC confiuration that always need to happen
> -	 * after a PHY or the CPU port comes up or down.
> -	 */
> -	if (!phydev->link) {
> -		int maxloop = 10;
> +static void vsc73xx_phylink_mac_link_down(struct dsa_switch *ds, int port,
> +					  unsigned int mode,
> +					  phy_interface_t interface)
> +{
> +	struct vsc73xx *vsc = ds->priv;
> +	u32 val;
>  
> -		dev_dbg(vsc->dev, "port %d: went down\n",
> -			port);
> +	int maxloop = VSC73XX_TABLE_ATTEMPTS;

Reverse christmas-tree for variable declarations, and there shouldn't
be a blank line between them. In any case, I don't think you need
"maxloop" if you adopt my suggestion below.

>  
> -		/* Disable RX on this port */
> -		vsc73xx_update_bits(vsc, VSC73XX_BLOCK_MAC, port,
> -				    VSC73XX_MAC_CFG,
> -				    VSC73XX_MAC_CFG_RX_EN, 0);
> +	dev_dbg(vsc->dev, "port %d: went down\n",
> +		port);
>  
> -		/* Discard packets */
> -		vsc73xx_update_bits(vsc, VSC73XX_BLOCK_ARBITER, 0,
> -				    VSC73XX_ARBDISC, BIT(port), BIT(port));
> +	/* Disable RX on this port */
> +	vsc73xx_update_bits(vsc, VSC73XX_BLOCK_MAC, port,
> +			    VSC73XX_MAC_CFG,
> +			    VSC73XX_MAC_CFG_RX_EN, 0);
> +
> +	/* Discard packets */
> +	vsc73xx_update_bits(vsc, VSC73XX_BLOCK_ARBITER, 0,
> +			    VSC73XX_ARBDISC, BIT(port), BIT(port));
>  
> -		/* Wait until queue is empty */
> +	/* Wait until queue is empty */
> +	vsc73xx_read(vsc, VSC73XX_BLOCK_ARBITER, 0,
> +		     VSC73XX_ARBEMPTY, &val);
> +	while (!(val & BIT(port))) {
> +		msleep(1);
>  		vsc73xx_read(vsc, VSC73XX_BLOCK_ARBITER, 0,
>  			     VSC73XX_ARBEMPTY, &val);
> -		while (!(val & BIT(port))) {
> -			msleep(1);
> -			vsc73xx_read(vsc, VSC73XX_BLOCK_ARBITER, 0,
> -				     VSC73XX_ARBEMPTY, &val);
> -			if (--maxloop == 0) {
> -				dev_err(vsc->dev,
> -					"timeout waiting for block arbiter\n");
> -				/* Continue anyway */
> -				break;
> -			}
> +		if (--maxloop == 0) {
> +			dev_err(vsc->dev,
> +				"timeout waiting for block arbiter\n");
> +			/* Continue anyway */
> +			break;
>  		}
> +	}

I know you're only moving this code, but I think it would be good to
_first_ have a patch that fixes this polling function:

	int ret, err;
...
		ret = read_poll_timeout(vsc73xx_read, err,
					err < 0 || (val & BIT(port)),
					1000, 10000, false,
					vsc, VSC73XX_BLOCK_ARBITER, 0,
					VSC73XX_ARBEMPTY, &val);
		if (ret != 0)
			dev_err(vsc->dev,
				"timeout waiting for block arbiter\n");
		else if (err < 0)
			dev_err(vsc->dev,
				"error reading arbiter\n");

This avoids the issue that on the last iteration, the code reads the
register, test it, find the condition that's being waiting for is
false, _then_ waits and end up printing the error message - that last
wait is rather useless, and as the arbiter state isn't checked after
waiting, it could be that we had success during the last wait.

> +static void vsc73xx_phylink_mac_link_up(struct dsa_switch *ds, int port,
> +					unsigned int mode,
> +					phy_interface_t interface,
> +					struct phy_device *phydev,
> +					int speed, int duplex,
> +					bool tx_pause, bool rx_pause)
> +{
> +	struct vsc73xx *vsc = ds->priv;
> +	u32 val;
>  
> +	switch (speed) {
> +	case SPEED_1000:
>  		/* Set up default for internal port or external RGMII */
> -		if (phydev->interface == PHY_INTERFACE_MODE_RGMII)
> +		if (interface == PHY_INTERFACE_MODE_RGMII)
>  			val = VSC73XX_MAC_CFG_1000M_F_RGMII;
>  		else
>  			val = VSC73XX_MAC_CFG_1000M_F_PHY;
> -		vsc73xx_adjust_enable_port(vsc, port, phydev, val);
> -	} else if (phydev->speed == SPEED_100) {
> -		if (phydev->duplex == DUPLEX_FULL) {
> -			val = VSC73XX_MAC_CFG_100_10M_F_PHY;
> -			dev_dbg(vsc->dev,
> -				"port %d: 100 Mbit full duplex mode\n",
> -				port);
> -		} else {
> -			val = VSC73XX_MAC_CFG_100_10M_H_PHY;
> -			dev_dbg(vsc->dev,
> -				"port %d: 100 Mbit half duplex mode\n",
> -				port);
> -		}
> -		vsc73xx_adjust_enable_port(vsc, port, phydev, val);
> -	} else if (phydev->speed == SPEED_10) {
> -		if (phydev->duplex == DUPLEX_FULL) {
> +		break;
> +	case SPEED_100:
> +	case SPEED_10:
> +		if (duplex == DUPLEX_FULL)
>  			val = VSC73XX_MAC_CFG_100_10M_F_PHY;
> -			dev_dbg(vsc->dev,
> -				"port %d: 10 Mbit full duplex mode\n",
> -				port);
> -		} else {
> +		else
>  			val = VSC73XX_MAC_CFG_100_10M_H_PHY;
> -			dev_dbg(vsc->dev,
> -				"port %d: 10 Mbit half duplex mode\n",
> -				port);
> -		}
> -		vsc73xx_adjust_enable_port(vsc, port, phydev, val);
> -	} else {
> -		dev_err(vsc->dev,
> -			"could not adjust link: unknown speed\n");
> +		break;
>  	}

Do the dev_dbg() add anything useful over what phylink prints when the
link comes up?

I don't think moving to a switch() statement for this is a good idea.
Given that "val" may be uninitialised, I suspect the following may be
a better solution:

	if (speed == SPEED_1000 || speed == SPEED_100 || speed == SPEED_10) {
		if (speed == SPEED_1000) {
			...
		} else {
			...
		}

		... set VSC73XX_BLOCK_ANALYZER and call
		vsc73xx_adjust_enable_port ...
	}

However, looking at the definitions of the various macros, it seems we
can do a little better by not using the VSC73XX_MAC_CFG_*M_[FH]_*
definitions:

		if (speed == SPEED_1000) {
			val = VSC73XX_MAC_CFG_GIGA_MODE |
			      VSC73XX_MAC_CFG_TX_IPG_1000M;

			if (interface == PHY_INTERFACE_MODE_RGMII)
				val |= VSC73XX_MAC_CFG_CLK_SEL_1000M;
			else
				val |= VSC73XX_MAC_CFG_CLK_SEL_EXT;
		} else {
			val = VSC73XX_MAC_CFG_TX_IPG_100_10M |
			      VSC73XX_MAC_CFG_CLK_SEL_EXT;
		}

		if (duplex == DUPLEX_FULL)
			val |= VSC73XX_MAC_CFG_FDX;

Now, this reveals a question: when operating in RGMII mode, why do we
need VSC73XX_MAC_CFG_CLK_SEL_1000M for 1G, and
VSC73XX_MAC_CFG_CLK_SEL_EXT for 10M and 100M, whereas "PHY" mode always
uses CLK_SEL_EXT ?

Thanks.

-- 
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