Re: [PATCH] Revert "arm64: dts: ls1028a: sl28: use ocelot-8021q tagging by default"

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Thu, Oct 27, 2022 at 01:32:48PM +0200, Michael Walle wrote:
> This reverts commit be0b178c50c37a666d54f435da71cf9f008362a0.
> 
> This commit will break networking on the sl28 boards if the tagger is
> not compiled into the kernel. If a non-default tagger is used, the
> kernel doesn't do a request_module(). Fixing that is also not that
> trivial because the tagger modules are loaded by ids, not by name.
> Thus for now, just revert to the default tagger until that is fixed.
> 
> Fixes: be0b178c50c3 ("arm64: dts: ls1028a: sl28: use ocelot-8021q tagging by default")
> Reported-by: Heiko Thiery <heiko.thiery@gmail.com>
> Signed-off-by: Michael Walle <michael@walle.cc>
> ---
> Vladimir, I'm not sure how to fix that one. Adding aliases to the tagger
> modules? Something like "MODULE_ALIAS("dsa_tag-ocelot-8021q");" and then do
> a request_module() in dsa_find_tagger_by_name(), too?
> 
>  .../arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28.dts | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28.dts b/arch/arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28.dts
> index 72429b37a8b4..771c50c7f50a 100644
> --- a/arch/arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28.dts
> +++ b/arch/arm64/boot/dts/freescale/fsl-ls1028a-kontron-sl28.dts
> @@ -324,14 +324,6 @@ &lpuart1 {
>  	status = "okay";
>  };
>  
> -&mscc_felix_port4 {
> -	dsa-tag-protocol = "ocelot-8021q";
> -};
> -
> -&mscc_felix_port5 {
> -	dsa-tag-protocol = "ocelot-8021q";
> -};
> -
>  &usb0 {
>  	status = "okay";
>  };
> -- 
> 2.30.2
>

Pretty nasty. Of all the switch drivers that support tagging protocol
change, Ocelot/Felix is the only one with this bug, because in all other
cases, the default and the alternative tagging protocol are part of the
same .ko. Only here we have tag_ocelot.ko and tag_ocelot_8021q.ko.

The problem preventing us from calling request_module() is that currently,
the string identifying the tagging protocol (to which we match device
tree information) is part of the tag_*.ko. I think we'd need the
translation table between string and enum dsa_tag_protocol to be part of
dsa_core.ko.