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

On 3/11/24 5:44 AM, Chintan Vankar wrote:

On 31/01/24 21:06, Andrew Davis wrote:

quoted

On 1/31/24 4:14 AM, Chintan Vankar wrote:

quoted

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?

quoted

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.

quoted

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

quoted

Andrew

quoted

---
  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 {

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