Re: [PATCH v4 2/6] arm64: dts: ti: k3-j784s4: Add alias to MCU CPSW2G

[Andrew Davis]

On 3/11/24 5:44 AM, Chintan Vankar wrote:
> On 31/01/24 21:06, Andrew Davis wrote:
> > On 1/31/24 4:14 AM, Chintan Vankar wrote:
> > > Add alias for the MCU CPSW2G port to enable Linux to fetch MAC Address
> > > for the port directly from U-Boot.
> >
> > Could you explain *how* this alias allows Linux to fetch a MAC
> > address from U-Boot? Sounds like we are doing something hacky here..
> Using "probe_daughtercards()" function U-Boot parses MAC addresses from
> EEPROM, then it internally calls "eth_env_set_enetaddr_by_index()"
> function which stores these MAC addresses into environment variables
> ethaddr, eth1addr, eth2addr and so on based on number of ports.
>
> U-Boot loads DTB during boot process, and it calls
> "fdt_fixup_ethernet()" function, which uses environment variables to
> update MAC addresses of ethernet ports as specified in the aliases
> section.

So maybe a better question would by why does it need to use aliases
for this?

> > Why can't Linux fetch the MAC from efuses the same way U-Boot does,
>
> Linux can fetch the MAC address from efuses if "ti,syscon-efuse"
> property is enabled.

Then let's do it this way always.

> > what happens if I don't use U-Boot to boot?
>
> If you don't use U-Boot to boot then the equivalent of
> "probe_daughtercards()" has to be implemented which is currently
> missing.

Or we just let Linux fetch it instead of implementing that function
in all the possible bootloaders. This would also remove a DTB fixup.
Those fixups should be avoided if at all possible.

Andrew

> > Andrew
> >
> > > ---
> > >   arch/arm64/boot/dts/ti/k3-j784s4-evm.dts | 1 +
> > >   1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/arm64/boot/dts/ti/k3-j784s4-evm.dts b/arch/arm64/boot/dts/ti/k3-j784s4-evm.dts
> > > index f34b92acc56d..b74f7d3025de 100644
> > > --- a/arch/arm64/boot/dts/ti/k3-j784s4-evm.dts
> > > +++ b/arch/arm64/boot/dts/ti/k3-j784s4-evm.dts
> > > @@ -27,6 +27,7 @@ aliases {
> > >           mmc1 = &main_sdhci1;
> > >           i2c0 = &wkup_i2c0;
> > >           i2c3 = &main_i2c0;
> > > +        ethernet0 = &mcu_cpsw_port1;
> > >       };
> > >       memory@80000000 {