On Thu, Aug 01, 2024 at 15:44, Vladimir Oltean <olteanv@xxxxxxxxx> wrote: > > Hi Pieter, > > On Thu, Aug 01, 2024 at 02:31:41PM +0200, vtpieter@xxxxxxxxx wrote: > > From: Pieter Van Trappen <pieter.van.trappen@xxxxxxx> > > > > Add and implement microchip,no-tag-protocol flag to allow disabling > > the switch' tagging protocol. For cases where the CPU MAC does not > > support MTU size > 1500 such as the Zynq GEM. > > > > This code was tested with a KSZ8794 chip. > > > > Pieter Van Trappen (2): > > dt-bindings: net: dsa: microchip: add microchip,no-tag-protocol flag > > net: dsa: microchip: implement microchip,no-tag-protocol flag > > > > .../devicetree/bindings/net/dsa/microchip,ksz.yaml | 5 +++++ > > drivers/net/dsa/microchip/ksz8795.c | 2 +- > > drivers/net/dsa/microchip/ksz9477.c | 2 +- > > drivers/net/dsa/microchip/ksz_common.c | 11 ++++++++--- > > drivers/net/dsa/microchip/ksz_common.h | 1 + > > drivers/net/dsa/microchip/lan937x_main.c | 2 +- > > 6 files changed, 17 insertions(+), 6 deletions(-) > > > > > > base-commit: 0a658d088cc63745528cf0ec8a2c2df0f37742d9 > > -- > > 2.43.0 > > Please use ./scripts/get_maintainer.pl when generating the To: and Cc: fields. > > Not to say that they don't exist, but I have never seen a NIC where MTU=1500 > is the absolute hard upper limit. How seriously did you study this before > determining that it is impossible to raise that? We're talking about one > byte for the tail tag, FWIW. > > There are also alternative paths to explore, like reducing the DSA user ports > MTU to 1499. This is currently not done when dev_set_mtu() fails on the conduit, > because Andrew said in the past it's likelier that the conduit is coded > to accept up to 1500 but will still work for small oversized packets. > > Disabling DSA tagging is a very heavy hammer, because it cuts off a whole lot > of functionality (the driver should no longer accept PTP hwtimestamping ioctls, > etc), so the patch set gets this tag from me currently, due to very shallow > justification: > > Nacked-by: Vladimir Oltean <olteanv@xxxxxxxxx> > > Please carry it forward if you choose to resubmit. Hi Vladimir, I do understand your reservation for this path, it defeats most of the advantages of DSA but I still do need the driver to handle the PHYs over SPI and for the WoL functionality; using the switch in a bridge configuration. My reason for mainlining is that I though there might be more people like me in a similar situation. This is actually an older issue and solution of mine so inspired by your comment I revisited the documentation and indeed hardware-wise I can't find back the MTU limitation. I see now that it's actually a limitation of the macb driver [1] so I will try to rework this one instead. Or implement `dsa-tag-protocol` as you propose. Or event better, both! Patch can be thus be cancelled, sorry for the spam. Cheers, Pieter [1]: https://elixir.bootlin.com/linux/v6.11-rc1/source/drivers/net/ethernet/cadence/macb_main.c#L5127
