netdev - Re: [PATCH net-next v2] ethtool: linkstate: add a statistic for PHY down events

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Date:   Fri, 28 Oct 2022 14:18:11 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        pabeni@...hat.com, corbet@....net, michael.chan@...adcom.com,
        hkallweit1@...il.com, linux@...linux.org.uk,
        huangguangbin2@...wei.com, chenhao288@...ilicon.com,
        moshet@...dia.com, linux@...pel-privat.de,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next v2] ethtool: linkstate: add a statistic for PHY
 down events

> @@ -67,6 +67,7 @@ static void phy_link_down(struct phy_device *phydev)
>  {
>  	phydev->phy_link_change(phydev, false);
>  	phy_led_trigger_change_speed(phydev);
> +	WRITE_ONCE(phydev->link_down_events, phydev->link_down_events + 1);

I'm not sure the WRITE_ONCE adds much value. Many systems using PHYLIB
are 32 bit, and i don't think WRITE_ONCE will make that 64 bit write
atomic on 32 bit systems. And as Florian pointed out, you have bigger
problems if you manged to overflow a u32 into a u64.

> @@ -723,6 +724,8 @@ struct phy_device {
>  
>  	int pma_extable;
>  
> +	unsigned int link_down_events;

And here is unsigned int, not u64? Or u32? It would be good to be
consistent.

> --- a/include/uapi/linux/ethtool_netlink.h
> +++ b/include/uapi/linux/ethtool_netlink.h
> @@ -262,6 +262,8 @@ enum {
>  	ETHTOOL_A_LINKSTATE_SQI_MAX,		/* u32 */
>  	ETHTOOL_A_LINKSTATE_EXT_STATE,		/* u8 */
>  	ETHTOOL_A_LINKSTATE_EXT_SUBSTATE,	/* u8 */
> +	ETHTOOL_A_LINKSTATE_PAD,
> +	ETHTOOL_A_LINKSTATE_EXT_DOWN_CNT,	/* u64 */

What is the PAD for?

     Andrew