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

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Date:   Thu, 28 Feb 2019 00:48:47 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Vivien Didelot <vivien.didelot@...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

On 28.02.2019 00:40, Vivien Didelot wrote:
> 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)
> 
OK

>> +		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.
> 
No, it's not a mask. I couldn't use 0 for "invalid" because 0 is used
otherwise, so I went with 0xff. All these STS_CMODE values are also
stored in mv88e6xxx_port.cmode that has type u8. Therefore I decided
to write it as an 8 bit value.

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