linux-kernel - Re: [PATCH net-next v2 2/2] net: xilinx: axienet: Add statistics support

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Message-ID: <f1837494-7411-463f-b9f6-fbdd09217423@linux.dev>
Date: Mon, 12 Aug 2024 16:25:16 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Andrew Lunn <andrew@...n.ch>
Cc: Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 netdev@...r.kernel.org, Simon Horman <horms@...nel.org>,
 Jakub Kicinski <kuba@...nel.org>, Russell King <linux@...linux.org.uk>,
 "David S . Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, Paolo Abeni <pabeni@...hat.com>,
 Michal Simek <michal.simek@....com>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next v2 2/2] net: xilinx: axienet: Add statistics
 support

On 8/12/24 16:22, Andrew Lunn wrote:
>>  static int __axienet_device_reset(struct axienet_local *lp)
>>  {
>>  	u32 value;
>>  	int ret;
>>  
>> +	/* Save statistics counters in case they will be reset */
>> +	guard(mutex)(&lp->stats_lock);
>> +	if (lp->features & XAE_FEATURE_STATS)
>> +		axienet_stats_update(lp, true);
> 
> My understanding of guard() is that the mutex is held until the
> function completes. That is much longer than you need. A
> scoped_guard() would be better here, and it makes it clear when the
> mutex will be released.

We have to hold it until...

>> +
>>  	/* Reset Axi DMA. This would reset Axi Ethernet core as well. The reset
>>  	 * process of Axi DMA takes a while to complete as all pending
>>  	 * commands/transfers will be flushed or completed during this
>> @@ -551,6 +595,23 @@ static int __axienet_device_reset(struct axienet_local *lp)
>>  		return ret;
>>  	}
>>  
>> +	/* Update statistics counters with new values */
>> +	if (lp->features & XAE_FEATURE_STATS) {
>> +		enum temac_stat stat;
>> +
>> +		write_seqcount_begin(&lp->hw_stats_seqcount);
>> +		lp->reset_in_progress = false;
>> +		for (stat = 0; stat < STAT_COUNT; stat++) {
>> +			u32 counter =
>> +				axienet_ior(lp, XAE_STATS_OFFSET + stat * 8);
>> +
>> +			lp->hw_stat_base[stat] +=
>> +				lp->hw_last_counter[stat] - counter;
>> +			lp->hw_last_counter[stat] = counter;
>> +		}
>> +		write_seqcount_end(&lp->hw_stats_seqcount);

...here

Which is effectively the whole function. The main reason why I used guard() was to
simplify the error return cases.

--Sean

>> +	}
>> +
>>  	return 0;
>>  }
>>  
> 
> 	Andrew