Messages in this thread | | | Date | Wed, 8 Sep 2021 16:36:00 -0700 | Subject | Re: Circular dependency between DSA switch driver and tagging protocol driver | From | Florian Fainelli <> |
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On 9/8/2021 3:19 PM, Vladimir Oltean wrote: > On Wed, Sep 08, 2021 at 03:14:51PM -0700, Florian Fainelli wrote: >> On 9/8/2021 3:08 PM, Vladimir Oltean wrote: >>> Hi, >>> >>> Since commits 566b18c8b752 ("net: dsa: sja1105: implement TX >>> timestamping for SJA1110") and 994d2cbb08ca ("net: dsa: tag_sja1105: be >>> dsa_loop-safe"), net/dsa/tag_sja1105.ko has gained a build and insmod >>> time dependency on drivers/net/dsa/sja1105.ko, due to several symbols >>> exported by the latter and used by the former. >>> >>> So first one needs to insmod sja1105.ko, then insmod tag_sja1105.ko. >>> >>> But dsa_port_parse_cpu returns -EPROBE_DEFER when dsa_tag_protocol_get >>> returns -ENOPROTOOPT. It means, there is no DSA_TAG_PROTO_SJA1105 in the >>> list of tagging protocols known by DSA, try again later. There is a >>> runtime dependency for DSA to have the tagging protocol loaded. Combined >>> with the symbol dependency, this is a de facto circular dependency. >>> >>> So when we first insmod sja1105.ko, nothing happens, probing is deferred. >>> >>> Then when we insmod tag_sja1105.ko, we expect the DSA probing to kick >>> off where it left from, and probe the switch too. >>> >>> However this does not happen because the deferred probing list in the >>> device core is reconsidered for a new attempt only if a driver is bound >>> to a new device. But DSA tagging protocols are drivers with no struct >>> device. >>> >>> One can of course manually kick the driver after the two insmods: >>> >>> echo spi0.1 > /sys/bus/spi/drivers/sja1105/bind >>> >>> and this works, but automatic module loading based on modaliases will be >>> broken if both tag_sja1105.ko and sja1105.ko are modules, and sja1105 is >>> the last device to get a driver bound to it. >>> >>> Where is the problem? >> >> I'd say with 994d2cbb08ca, since the tagger now requires visibility into >> sja1105_switch_ops which is not great, to say the least. You could solve >> this by: >> >> - splitting up the sja1150 between a library that contains >> sja1105_switch_ops and does not contain the driver registration code >> >> - finding a different way to do a dsa_switch_ops pointer comparison, by >> e.g.: maintaining a boolean in dsa_port that tracks whether a particular >> driver is backing that port > > What about 566b18c8b752 ("net: dsa: sja1105: implement TX timestamping for SJA1110")? > It is essentially the same problem from a symbol usage perspective, plus > the fact that an skb queue belonging to the driver is accessed.
I believe we will have to accept that another indirect function call must be made in order to avoid creating a direct symbol dependency with sja1110_rcv_meta() would that be acceptable performance wise? -- Florian
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