Re: [PATCH v3 net-next 06/11] net: dsa: kill .port_egress_floods overengineering

From: Florian Fainelli <f.fainelli@gmail.com>
To: Vladimir Oltean <olteanv@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>,
	"David S. Miller" <davem@davemloft.net>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	bridge@lists.linux-foundation.org,
	Roopa Prabhu <roopa@nvidia.com>,
	Nikolay Aleksandrov <nikolay@nvidia.com>,
	Jiri Pirko <jiri@resnulli.us>, Ido Schimmel <idosch@idosch.org>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	UNGLinuxDriver@microchip.com, Vadym Kochan <vkochan@marvell.com>,
	Taras Chornyi <tchornyi@marvell.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Ioana Ciornei <ioana.ciornei@nxp.com>,
	Ivan Vecera <ivecera@redhat.com>,
	linux-omap@vger.kernel.org
Subject: Re: [PATCH v3 net-next 06/11] net: dsa: kill .port_egress_floods overengineering
Date: Wed, 10 Feb 2021 20:18:27 -0800	[thread overview]
Message-ID: <fa66ce8e-4292-808a-e9ee-4a0afd2d32ce@gmail.com> (raw)
In-Reply-To: <20210210091445.741269-7-olteanv@gmail.com>


On 2/10/2021 1:14 AM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> 
> The bridge offloads the port flags through a single bit mask using
> switchdev, which among others, contains learning and flooding settings.
> 
> The commit 57652796aa97 ("net: dsa: add support for bridge flags")
> missed one crucial aspect of the SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS API
> when designing the API one level lower, towards the drivers.
> This is that the bitmask of passed brport flags never has more than one
> bit set at a time. On the other hand, the prototype passed to the driver
> is .port_egress_floods(int port, bool unicast, bool multicast), which
> configures two flags at a time.
> 
> DSA currently checks if .port_egress_floods is implemented, and if it
> is, reports both BR_FLOOD and BR_MCAST_FLOOD as supported. So the driver
> has no choice if it wants to inform the bridge that, for example, it
> can't configure unicast flooding independently of multicast flooding -
> the DSA mid layer is standing in the way. Or the other way around: a new
> driver wants to start configuring BR_BCAST_FLOOD separately, but what do
> we do with the rest, which only support unicast and multicast flooding?
> Do we report broadcast flooding configuration as supported for those
> too, and silently do nothing?
> 
> Secondly, currently DSA deems the driver too dumb to deserve knowing that
> a SWITCHDEV_ATTR_ID_BRIDGE_MROUTER attribute was offloaded, because it
> just calls .port_egress_floods for the CPU port. When we'll add support
> for the plain SWITCHDEV_ATTR_ID_PORT_MROUTER, that will become a real
> problem because the flood settings will need to be held statefully in
> the DSA middle layer, otherwise changing the mrouter port attribute will
> impact the flooding attribute. And that's _assuming_ that the underlying
> hardware doesn't have anything else to do when a multicast router
> attaches to a port than flood unknown traffic to it. If it does, there
> will need to be a dedicated .port_set_mrouter anyway.
> 
> Lastly, we have DSA drivers that have a backlink into a pure switchdev
> driver (felix -> ocelot). It seems reasonable that the other switchdev
> drivers should not have to suffer from the oddities of DSA overengineering,
> so keeping DSA a pass-through layer makes more sense there.
> 
> To simplify the brport flags situation we just delete .port_egress_floods
> and we introduce a simple .port_bridge_flags which is passed to the
> driver. Also, the logic from dsa_port_mrouter is removed and a
> .port_set_mrouter is created.
> 
> Functionally speaking, we simply move the calls to .port_egress_floods
> one step lower, in the two drivers that implement it: mv88e6xxx and b53,
> so things should work just as before.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

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