netdev - Re: [PATCH net] net: dsa: mv88e6xxx: prevent interrupt storm caused by mv88e6390x_port_set

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Message-ID: <20190227184040.GB23759@t480s.localdomain>
Date:   Wed, 27 Feb 2019 18:40:40 -0500
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: dsa: mv88e6xxx: prevent interrupt storm caused
 by mv88e6390x_port_set_cmode

Hi Heiner,

On Wed, 27 Feb 2019 20:55:22 +0100, Heiner Kallweit <hkallweit1@...il.com> wrote:
> When debugging another issue I faced an interrupt storm in this
> driver (88E6390, port 9 in SGMII mode), consisting of alternating
> link-up / link-down interrupts. Analysis showed that the driver
> wanted to set a cmode that was set already. But so far
> mv88e6390x_port_set_cmode() doesn't check this and powers down
> SERDES, what causes the link to break, and eventually results in
> the described interrupt storm.
> 
> Fix this by checking whether the cmode actually changes. We want
> that the very first call to mv88e6390x_port_set_cmode() always
> configures the registers, therefore initialize port.cmode with
> a value that is different from any supported cmode value.
> 
> Fixes: 364e9d7776a3 ("net: dsa: mv88e6xxx: Power on/off SERDES on cmode change")
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/dsa/mv88e6xxx/chip.c | 4 ++++
>  drivers/net/dsa/mv88e6xxx/port.c | 4 ++++
>  drivers/net/dsa/mv88e6xxx/port.h | 1 +
>  3 files changed, 9 insertions(+)
> 
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index 32e7af5ca..d4edb61e8 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -4568,6 +4568,7 @@ static int mv88e6xxx_detect(struct mv88e6xxx_chip *chip)
>  static struct mv88e6xxx_chip *mv88e6xxx_alloc_chip(struct device *dev)
>  {
>  	struct mv88e6xxx_chip *chip;
> +	int i;
>  
>  	chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
>  	if (!chip)
> @@ -4578,6 +4579,9 @@ static struct mv88e6xxx_chip *mv88e6xxx_alloc_chip(struct device *dev)
>  	mutex_init(&chip->reg_lock);
>  	INIT_LIST_HEAD(&chip->mdios);
>  
> +	for (i = 0; i < ARRAY_SIZE(chip->ports); i++)

                        mv88e6xxx_num_ports(chip)

> +		chip->ports[i].cmode = MV88E6XXX_PORT_STS_CMODE_INVALID;
> +
>  	return chip;
>  }
>  
> diff --git a/drivers/net/dsa/mv88e6xxx/port.c b/drivers/net/dsa/mv88e6xxx/port.c
> index ebd26b6a9..70b7a1463 100644
> --- a/drivers/net/dsa/mv88e6xxx/port.c
> +++ b/drivers/net/dsa/mv88e6xxx/port.c
> @@ -398,6 +398,10 @@ int mv88e6390x_port_set_cmode(struct mv88e6xxx_chip *chip, int port,
>  		cmode = 0;
>  	}
>  
> +	/* cmode doesn't change, nothing to do for us */
> +	if (cmode == chip->ports[port].cmode)
> +		return 0;
> +
>  	lane = mv88e6390x_serdes_get_lane(chip, port);
>  	if (lane < 0)
>  		return lane;
> diff --git a/drivers/net/dsa/mv88e6xxx/port.h b/drivers/net/dsa/mv88e6xxx/port.h
> index e583641de..4aadf321e 100644
> --- a/drivers/net/dsa/mv88e6xxx/port.h
> +++ b/drivers/net/dsa/mv88e6xxx/port.h
> @@ -52,6 +52,7 @@
>  #define MV88E6185_PORT_STS_CMODE_1000BASE_X	0x0005
>  #define MV88E6185_PORT_STS_CMODE_PHY		0x0006
>  #define MV88E6185_PORT_STS_CMODE_DISABLED	0x0007
> +#define MV88E6XXX_PORT_STS_CMODE_INVALID	0xff

Is this 0xff a mask value from the Port Status register? If so please
the 0x1234 format like above, to make this mask value obvious.

>  
>  /* Offset 0x01: MAC (or PCS or Physical) Control Register */
>  #define MV88E6XXX_PORT_MAC_CTL				0x01


Thanks,

	Vivien