linux-kernel - Re: [PATCH] net: fec: turn on device when extracting statistics

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Message-Id: <20161128.091149.2039527154584013771.davem@davemloft.net>
Date:   Mon, 28 Nov 2016 09:11:49 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     nikita.yoush@...entembedded.com
Cc:     fugang.duan@....com, troy.kisky@...ndarydevices.com,
        andrew@...n.ch, eric@...int.com, tremyfr@...il.com,
        johannes@...solutions.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, cphealy@...il.com,
        fabio.estevam@....com
Subject: Re: [PATCH] net: fec: turn on device when extracting statistics

From: Nikita Yushchenko <nikita.yoush@...entembedded.com>
Date: Mon, 28 Nov 2016 10:06:31 +0300

> 
> 
> 28.11.2016 04:29, David Miller пишет:
>> From: Nikita Yushchenko <nikita.yoush@...entembedded.com>
>> Date: Fri, 25 Nov 2016 13:02:00 +0300
>> 
>>> +	int i, ret;
>>> +
>>> +	ret = pm_runtime_get_sync(&fep->pdev->dev);
>>> +	if (IS_ERR_VALUE(ret)) {
>>> +		memset(data, 0, sizeof(*data) * ARRAY_SIZE(fec_stats));
>>> +		return;
>>> +	}
>> 
>> This really isn't the way to do this.
>> 
>> When the device is suspended and the clocks are going to be stopped,
>> you must fetch the statistic values into a software copy and provide
>> those if the device is suspended when statistics are requested.
> 
> Ok, can do that, although can't see what's wrong with waking device
> here. The situation of requesting stats on down device isn't something
> widely used, thus keeping handling of that as local as possible looks
> better for me.

The issue is the fact that you need error handling at all and might
therefore provide a set of zero stats to the user when that entire
possibility could have been avoided in the first place by recording
the stats at suspend time.