netdev - Re: [PATCH net-next v2 18/21] net: ravb: Return cached statistics if the interface is down

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Date: Sat, 16 Dec 2023 23:02:24 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Claudiu <claudiu.beznea@...on.dev>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<richardcochran@...il.com>, <p.zabel@...gutronix.de>,
	<yoshihiro.shimoda.uh@...esas.com>, <wsa+renesas@...g-engineering.com>,
	<geert+renesas@...der.be>
CC: <netdev@...r.kernel.org>, <linux-renesas-soc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH net-next v2 18/21] net: ravb: Return cached statistics if
 the interface is down

On 12/14/23 2:45 PM, Claudiu wrote:

> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> Return the cached statistics in case the interface is down. There should be
> no drawback to this, as most of the statistics are updated on the data path
> and if runtime PM is enabled and the interface is down, the registers that
> are explicitly read on ravb_get_stats() are zero anyway on most of the IP
> variants.
> 
> The commit prepares the code for the addition of runtime PM support.
> 
> Suggested-by: Sergey Shtylyov <s.shtylyov@....ru>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---
> 
> Changes in v2:
> - none; this patch is new
> 
>  drivers/net/ethernet/renesas/ravb_main.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index a2a64c22ec41..1995cf7ff084 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -2110,6 +2110,9 @@ static struct net_device_stats *ravb_get_stats(struct net_device *ndev)
>  	const struct ravb_hw_info *info = priv->info;
>  	struct net_device_stats *nstats, *stats0, *stats1;
>  
> +	if (!netif_running(ndev))

   I'm afraid this is racy as __LINK_STATE_START bit gets set
by __dev_open() before calling the ndo_open() method... :-(

> +		return &ndev->stats;
> +

   The sh_eth driver calls sh_eth_get_stats() from sh_eth_dev_exit();
perhaps it's worth doing something similar?

MBR, Sergey