Message-ID: <20220905205226.hwrnjx6qnrkdjw76@skbuf>
Date:   Mon, 5 Sep 2022 20:52:27 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Hongbo Wang <hongbo.wang@....com>
CC:     Andrew Lunn <andrew@...n.ch>, Hongjun Chen <hongjun.chen@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Walle <michael@...le.cc>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>
Subject: Re: [PATCH v1] arm64: dts: fsl: ls1028a-rdb: Add dts file to choose
 swp5 as dsa master

On Tue, Aug 17, 2021 at 02:59:07AM +0000, Hongbo Wang wrote:
> > On Mon, Aug 16, 2021 at 06:03:52AM +0000, Hongbo Wang wrote:
> > > > I was going to suggest as an alternative to define a device tree
> > > > overlay file with the changes in the CPU port assignment, instead of
> > > > defining a wholly new DTS for the LS1028A reference design board.
> > > > But I am pretty sure that it is not possible to specify a
> > > > /delete-property/ inside a device tree overlay file, so that won't actually work.
> > >
> > > hi Vladimir,
> > >
> > >   if don't specify "/delete-property/" in this dts file, the
> > > corresponding dtb will not work well, so I add it to delete 'ethernet' property
> > > from mscc_felix_port4 explicitly.
> >
> > Judging by the reply, I am not actually sure you've understood what has been
> > said.
> >
> > I said:
> >
> > There is an option to create a device tree overlay:
> >
> > https://www.kernel.org/doc/html/latest/devicetree/overlay-notes.html
> >
> > We use these for the riser cards on the LS1028A-QDS boards.
> >
> > https://source.codeaurora.org/external/qoriq/qoriq-components/linux/tree/ar
> > ch/arm64/boot/dts/freescale/fsl-ls1028a-qds-13bb.dts?h=LSDK-20.12-V5.4
> >
> > They are included as usual in a U-Boot ITB file:
> >
> > / {
> >       images {
> >               /* Base DTB */
> >               ls1028aqds-dtb {
> >                       description = "ls1028aqds-dtb";
> >                       data = /incbin/("arch/arm64/boot/dts/freescale/fsl-ls1028a-qds.dtb");
> >                       type = "flat_dt";
> >                       arch = "arm64";
> >                       os = "linux";
> >                       compression = "none";
> >                       load = <0x90000000>;
> >                       hash@1 {
> >                               algo = "crc32";
> >                       };
> >               };
> >               /* Overlay */
> >               fdt@...028aqds-13bb {
> >                       description = "ls1028aqds-13bb";
> >                       data = /incbin/("arch/arm64/boot/dts/freescale/fsl-ls1028a-qds-13bb.dtb");
> >                       type = "flat_dt";
> >                       arch = "arm64";
> >                       load = <0x90010000>;
> >               };
> >       };
> > };
> >
> > In U-Boot, you apply the overlay as following:
> >
> > tftp $kernel_addr_r boot.itb && bootm
> > $kernel_addr_r#ls1028aqds#ls1028aqds-13bb
> >
> > It would have been nice to have a similar device tree overlay that changes the
> > DSA master from eno2 to eno3, and for that overlay to be able to be applied
> > (or not) from U-Boot.
> >
> > But it's _not_ possible, because you cannot put the /delete-property/ (that you
> > need to have) in the .dtbo file. Or if you put it, it will not delete the property
> > from the base dtb.
> >
> > That's all I said.
> 
> thanks for the detailed explanation,
> I have got your point.
> 
> thanks,
> hongbo

I'm replying to a very old topic here, but I don't think this made too
much progress (NXP still carries a downstream fsl-ls1028a-rdb-dsa-swp5-eno3.dts,
for a use case which is valid: using one of the 2 internal Ethernet
ports between the switch and the SoC as a plain data port, rather than a
CPU port).

I've found what I think is a satisfactory solution for myself. Rather
than carrying an entirely new device tree just to move around the DSA
master from &enetc_port2 to &enetc_port3, I'm building upon the changes
for multiple CPU ports which Shawn has accepted now.
https://lore.kernel.org/linux-arm-kernel/20220831160124.914453-1-olteanv@gmail.com/

With that patch set, what Hongbo tried to add here simply becomes:

&mscc_felix_port4 {
	/delete-property/ ethernet;
};

I've already expressed discontent with the fact that it isn't possible
to move just this action to a device tree overlay and apply it to
whatever LS1028A based board, not just the RDB. However, I found that it
is possible to do this instead, just from within the U-Boot shell:

fdt addr $fdt_addr_r
fdt rm /soc/pcie@...000000/ethernet-switch@0,5/ports/port@4 ethernet
...
bootm $kernel_addr_r - $fdt_addr_r

which is even more convenient, because this way, the board device trees
now don't even need to be compiled with the dtc "-@" option (to include
the __symbols__ node required for dtb overlays).

It's likely that some of the people copied here do fancier tricks with
dynamic editing of the FDT already, on a day by day basis. In that case,
what can I say, have a good rest of the day ;)

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