netdev - Re: [PATCH net-next v2 1/7] net: dsa: mt7530: always trap frames to active CPU port on MT7530

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Date: Thu, 4 Jan 2024 17:22:32 +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>,
	Russell King <linux@...linux.org.uk>,
	Frank Wunderlich <frank-w@...lic-files.de>,
	Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
	mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next v2 1/7] net: dsa: mt7530: always trap frames to
 active CPU port on MT7530

On Wed, Dec 27, 2023 at 07:43:41AM +0300, Arınç ÜNAL wrote:
> On the MT7530 switch, the CPU_PORT field indicates which CPU port to trap
> frames to, regardless of the affinity of the inbound user port.
> 
> When multiple CPU ports are in use, if the DSA conduit interface is down,
> trapped frames won't be passed to the conduit interface.
> 
> To make trapping frames work including this case, implement
> ds->ops->master_state_change() on this subdriver and set the CPU_PORT field

conduit_state_change()

> to the numerically smallest CPU port which the DSA conduit interface its
> affine to is up. Introduce the active_cpu_ports field to store the
> information of the active CPU ports. Correct the macros, CPU_PORT is bits 4
> through 6 of the register.
> 
> Add a comment to explain frame trapping for this switch.
> 
> Currently, the driver doesn't support the use of multiple CPU ports so this
> is not necessarily a bug fix.
> 
> Suggested-by: Vladimir Oltean <olteanv@...il.com>
> Suggested-by: Russell King (Oracle) <linux@...linux.org.uk>
> Signed-off-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> ---
>  drivers/net/dsa/mt7530.c | 37 +++++++++++++++++++++++++++++++++----
>  drivers/net/dsa/mt7530.h |  6 ++++--
>  2 files changed, 37 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index 391c4dbdff42..436d5c311be0 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -1035,10 +1035,6 @@ mt753x_cpu_port_enable(struct dsa_switch *ds, int port)
>  	mt7530_set(priv, MT7530_MFC, BC_FFP(BIT(port)) | UNM_FFP(BIT(port)) |
>  		   UNU_FFP(BIT(port)));
>  
> -	/* Set CPU port number */
> -	if (priv->id == ID_MT7530 || priv->id == ID_MT7621)
> -		mt7530_rmw(priv, MT7530_MFC, CPU_MASK, CPU_EN | CPU_PORT(port));
> -
>  	/* Add the CPU port to the CPU port bitmap for MT7531 and the switch on
>  	 * the MT7988 SoC. Trapped frames will be forwarded to the CPU port that
>  	 * is affine to the inbound user port.
> @@ -3075,6 +3071,38 @@ static int mt753x_set_mac_eee(struct dsa_switch *ds, int port,
>  	return 0;
>  }
>  
> +static void
> +mt753x_conduit_state_change(struct dsa_switch *ds,
> +			    const struct net_device *conduit,
> +			    bool operational)
> +{
> +	struct dsa_port *cpu_dp = conduit->dsa_ptr;
> +	struct mt7530_priv *priv = ds->priv;
> +	u8 mask;
> +	int val = 0;

Longest line first.

> +
> +	/* 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.

"first CPU port whose conduit interface is up"

> +	 */
> +	if (priv->id != ID_MT7530 && priv->id != ID_MT7621)
> +		return;
> +
> +	mask = BIT(cpu_dp->index);
> +
> +	if (operational)
> +		priv->active_cpu_ports |= mask;
> +	else
> +		priv->active_cpu_ports &= ~mask;
> +
> +	if (priv->active_cpu_ports)
> +		val =
> +		    CPU_EN |
> +		    CPU_PORT(__ffs((unsigned long)priv->active_cpu_ports));

I don't think the type cast is necessary (implicit type promotion takes place).

Also, it is customary to put {} for multi-line "if" blocks, even if they are
made up of a single expression.

But without the type cast, it could look like this.

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

> +
> +	mt7530_rmw(priv, MT7530_MFC, CPU_EN | CPU_PORT_MASK, val);
> +}