Subject: Re: [PATCH net-next 01/15] net: dsa: mt7530: always trap frames to active CPU port on MT7530

From: "Russell King (Oracle)" <[email-masked]>
Date: Sat, 18 Nov 2023 14:34:55 +0000

On Sat, Nov 18, 2023 at 03:31:51PM +0300, Arınç ÜNAL wrote:
> +	/* Set the CPU port to trap frames to for MT7530. Trapped frames will be
> +	 * forwarded to the numerically smallest CPU port which the DSA conduit
> +	 * interface its affine to is up.
> +	 */
> +	if (priv->id != ID_MT7530 && priv->id != ID_MT7621)
> +		return;
> +
> +	if (operational)
> +		priv->active_cpu_ports |= BIT(cpu_dp->index);
> +	else
> +		priv->active_cpu_ports &= ~BIT(cpu_dp->index);
> +
> +	if (priv->active_cpu_ports)
> +		mt7530_rmw(priv, MT7530_MFC, CPU_EN | CPU_PORT_MASK, CPU_EN |
> +			   CPU_PORT(__ffs(priv->active_cpu_ports)));

I would be tempted to write this as:

	mask = BIT(cpu_dp->index);

	if (operational)
		priv->active_cpu_ports |= mask;
	else
		priv->active_cpu_ports &= ~mask;

Now, what happens when active_cpu_ports is zero? Doesn't that mean there
is no active CPU port? In which case, wouldn't disabling the CPU port
direction be appropriate, such as:

	if (priv->active_cpu_ports)
		val = CPU_EN | CPU_PORT(__ffs(priv->active_cpu_ports));
	else
		val = 0;

	mt7530_rmw(priv, MT7530_MFC, CPU_EN | CPU_PORT_MASK, val);	

?

>  struct mt7530_priv {
>  	struct device		*dev;
> @@ -786,6 +787,7 @@ struct mt7530_priv {
>  	struct irq_domain *irq_domain;
>  	u32 irq_enable;
>  	int (*create_sgmii)(struct mt7530_priv *priv, bool dual_sgmii);
> +	unsigned long active_cpu_ports;

So this will be 32 or 64 bit in size. Presumably you know how many CPU
ports there can be, which looking at this code must be less than 8 as
CPU_PORT_MASK is only 3 bits in size. So, maybe use a u8, and check
that cpu_dp->index <= 7 ?

I would also suggest moving irq_enable after create_sgmii, to avoid
holes in the struct.

-- 
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