netdev - Re: [RFC PATCH v7 01/16] net: dsa: provide switch operations for tracking the master state

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Date:   Tue, 25 Jan 2022 19:22:51 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC PATCH v7 01/16] net: dsa: provide switch operations for
 tracking the master state



On 1/22/2022 5:33 PM, Ansuel Smith wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> Certain drivers may need to send management traffic to the switch for
> things like register access, FDB dump, etc, to accelerate what their
> slow bus (SPI, I2C, MDIO) can already do.
> 
> Ethernet is faster (especially in bulk transactions) but is also more
> unreliable, since the user may decide to bring the DSA master down (or
> not bring it up), therefore severing the link between the host and the
> attached switch.
> 
> Drivers needing Ethernet-based register access already should have
> fallback logic to the slow bus if the Ethernet method fails, but that
> fallback may be based on a timeout, and the I/O to the switch may slow
> down to a halt if the master is down, because every Ethernet packet will
> have to time out. The driver also doesn't have the option to turn off
> Ethernet-based I/O momentarily, because it wouldn't know when to turn it
> back on.
> 
> Which is where this change comes in. By tracking NETDEV_CHANGE,
> NETDEV_UP and NETDEV_GOING_DOWN events on the DSA master, we should know
> the exact interval of time during which this interface is reliably
> available for traffic. Provide this information to switches so they can
> use it as they wish.
> 
> An helper is added dsa_port_master_is_operational() to check if a master
> port is operational.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian