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Date: Mon, 18 Sep 2017 16:48:56 -0700 From: Florian Fainelli <f.fainelli@...il.com> To: Tristram.Ha@...rochip.com, andrew@...n.ch Cc: muvarov@...il.com, pavel@....cz, nathan.leigh.conrad@...il.com, vivien.didelot@...oirfairelinux.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Woojung.Huh@...rochip.com Subject: Re: [PATCH RFC 6/6] Modify tag_ksz.c to support other KSZ switch drivers On 09/18/2017 04:44 PM, Tristram.Ha@...rochip.com wrote: >>> In the old DSA implementation all the ports are partitioned into its own >> device >>> and the bridge joining them will do all the forwarding. This is useful for >> quick >>> testing with some protocols like RSTP but it is probably useless for real >>> operation. >> >> It is a good minimal driver, to get something into the kernel. You can >> then add features to it. >> >>> The new switchdev model tries to use the switch hardware as much as >>> possible. This offload_fwd_mark bit means the frame is forwarded by the >>> hardware switch, so the software bridge does not need to do it again. >> Without >>> this bit there will be duplicated multicast frames coming out the ports if >> internal >>> forwarding is enabled. >> >> Correct. Once you switch driver is clever enough, you can enable >> offload_fwd_mark. >> >>> When RSTP is used the port can be put in blocked state and so the >> forwarding >>> will stop for that port. Currently the switch driver will check that >> membership >>> to decide whether to set that bit. >> >> This i don't get. RSTP or STP just break loops. How does RSTP vs STP >> mean you need to set offload_fwd_mark differently? >> > > The logic of the switch driver is if the membership of the port receiving > the frame contains other ports--not counting cpu port--the bit > offload_fwd_mark is set. In RSTP closing the blocked port is generally good > enough, but there are exceptions, so the port is removed from the > membership of other forwarding ports. A disabled port will have its > membership completely reset so it cannot receive anything. It does not > matter much in RSTP as the software bridge should know whether to forward > the frame or not. > > We are back to square one. Is there any plan to add this offload_fwd_mark > support to DSA driver so that it can be reported properly? It can be set all the > time, except during port initialization or before bridge creation the forwarding > state does not reflect reality. > > If not the port membership can be fixed and there is no internal switch > forwarding, leaving everything handled by the software bridge. I am not really sure why this is such a concern for you so soon when your driver is not even included yet. You should really aim for baby steps here: get the basic driver(s) included, with a limited set of features, and gradually add more features to the driver. When fwd_offload_mark and RSTP become a real problem, we can most definitively find a way to fix those in DSA and depending drivers. -- Florian
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