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

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Date: Sat, 18 Nov 2023 14:34:55 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
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>,
	Vladimir Oltean <olteanv@...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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	Frank Wunderlich <frank-w@...lic-files.de>,
	Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
	mithat.guner@...ont.com, erkin.bozoglu@...ont.com
Subject: Re: [PATCH net-next 01/15] net: dsa: mt7530: always trap frames to
 active CPU port on MT7530

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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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