netdev - Re: [PATCH net-next 1/2] ethtool: add PHY Fast Link Down support

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Message-ID: <20190325174928.GF26076@unicorn.suse.cz>
Date:   Mon, 25 Mar 2019 18:49:28 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "John W. Linville" <linville@...driver.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] ethtool: add PHY Fast Link Down support

On Sun, Mar 24, 2019 at 04:02:43PM +0100, Heiner Kallweit wrote:
> This adds support for Fast Link Down as new PHY tunable.
> Fast Link Down reduces the time until a link down event is reported
> for 1000BaseT. According to the standard it's 750ms what is too long
> for several use cases.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  include/uapi/linux/ethtool.h | 4 ++++
>  net/core/ethtool.c           | 2 ++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
> index 3652b239d..2c7136adc 100644
> --- a/include/uapi/linux/ethtool.h
> +++ b/include/uapi/linux/ethtool.h
> @@ -252,9 +252,13 @@ struct ethtool_tunable {
>  #define DOWNSHIFT_DEV_DEFAULT_COUNT	0xff
>  #define DOWNSHIFT_DEV_DISABLE		0
>  
> +#define ETHTOOL_PHY_FAST_LINK_DOWN_ON	0
> +#define ETHTOOL_PHY_FAST_LINK_DOWN_OFF	0xff
> +
>  enum phy_tunable_id {
>  	ETHTOOL_PHY_ID_UNSPEC,
>  	ETHTOOL_PHY_DOWNSHIFT,
> +	ETHTOOL_PHY_FAST_LINK_DOWN,
>  	/*
>  	 * Add your fresh new phy tunable attribute above and remember to update
>  	 * phy_tunable_strings[] in net/core/ethtool.c

It would be nice to have a short summary around here explaining how is
the value interpreted. While it's obvious from the second patch, one
shouldn't have to go into driver specific implementation to find out.

I also wonder if the range 0-254 ms is sufficient. Would it be possible
that there is some other hardware which would support e.g. 300 ms?

Michal Kubecek

> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index b1eb32419..387d67eb7 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -136,6 +136,7 @@ static const char
>  phy_tunable_strings[__ETHTOOL_PHY_TUNABLE_COUNT][ETH_GSTRING_LEN] = {
>  	[ETHTOOL_ID_UNSPEC]     = "Unspec",
>  	[ETHTOOL_PHY_DOWNSHIFT]	= "phy-downshift",
> +	[ETHTOOL_PHY_FAST_LINK_DOWN] = "phy-fast-link-down",
>  };
>  
>  static int ethtool_get_features(struct net_device *dev, void __user *useraddr)
> @@ -2432,6 +2433,7 @@ static int ethtool_phy_tunable_valid(const struct ethtool_tunable *tuna)
>  {
>  	switch (tuna->id) {
>  	case ETHTOOL_PHY_DOWNSHIFT:
> +	case ETHTOOL_PHY_FAST_LINK_DOWN:
>  		if (tuna->len != sizeof(u8) ||
>  		    tuna->type_id != ETHTOOL_TUNABLE_U8)
>  			return -EINVAL;
> -- 
> 2.21.0
> 
>