netdev - Re: [RFC net-next PATCH 3/3] mv88e6xxx: rmon: Use RMU to collect rmon data.

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Message-ID: <00b2d570-a9a9-244c-51ca-7363b9a74aec@gmail.com>
Date:   Fri, 19 Aug 2022 07:47:48 +0200
From:   Mattias Forsblad <mattias.forsblad@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, Vivien Didelot <vivien.didelot@...il.com>,
        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>
Subject: Re: [RFC net-next PATCH 3/3] mv88e6xxx: rmon: Use RMU to collect rmon
 data.

On 2022-08-18 17:36, Andrew Lunn wrote:
>> @@ -1310,16 +1323,22 @@ static void mv88e6xxx_get_ethtool_stats(struct dsa_switch *ds, int port,
>>  	struct mv88e6xxx_chip *chip = ds->priv;
>>  	int ret;
>>  
>> -	mv88e6xxx_reg_lock(chip);
>> +	if (chip->rmu.ops && chip->rmu.ops->get_rmon) {
>> +		ret = chip->rmu.ops->get_rmon(chip, port, data);
>> +		if (ret == -ETIMEDOUT)
>> +			return;
>> +	} else {
>>  
>> -	ret = mv88e6xxx_stats_snapshot(chip, port);
>> -	mv88e6xxx_reg_unlock(chip);
>> +		mv88e6xxx_reg_lock(chip);
>>  
>> -	if (ret < 0)
>> -		return;
>> +		ret = mv88e6xxx_stats_snapshot(chip, port);
>> +		mv88e6xxx_reg_unlock(chip);
>>  
>> -	mv88e6xxx_get_stats(chip, port, data);
>> +		if (ret < 0)
>> +			return;
>>  
>> +		mv88e6xxx_get_stats(chip, port, data);
>> +	}
>>  }
> 
> I don't particularly like the way this is all mixed together.
> 
> Could you try to split it, so there is an MDIO set of functions and an
> RMU set of functions. Maybe you have some helpers which are used by
> both.
> 

I think that a great idea. Will split in separate functions.

> I would also suggest you try to think about ATU dump and VTU dump. You
> ideally want a code structure which is very similar for all these dump
> operations. Take a look at how qca8k-8xxx.c does things.
> 

I think that the ATU dump is the logical next step to implement. I'll
have a look in qca8k to see how they do things.

AFAIK there is no RMU operation for VTU dump. That needs to be done 
with register reads and writes.

> Is it documented in the datasheet that when RMU is used a snapshot is
> not required?
> 
>     Andrew

In the documentation they only mention captured counters with regards 
to MDIO accesses. I cannot see that that is necessary with RMU.
FYI on our board the time delta between request and reply 
is ~100us (which is nice)