dwc: Add support for the cvitek ethernet controller

[bnovkov]

Summary

This patch adds support for the cvitek flavor of the DWC ethernet
controller. This controller is present on the Milk-V riscv SoCs.

Test Plan

I've been running this patch on a Milk-V Duo S board for a week and didn't run into any issues so far.

[manu]

You should add the file to one of the std.XXX file in sys/riscv/conf

sys/dev/dwc/if_dwc_cvitek.c

80

No syscon handle in the device dtb node ?

[bnovkov]

Address @manu 's comments.

[bnovkov]

In D48530#1107313, @manu wrote:

You should add the file to one of the std.XXX file in sys/riscv/conf

Ah sorry, my differential uploading spree was interrupted before I could do that, D48533 should take care of that.

sys/dev/dwc/if_dwc_cvitek.c

80

No, but it does make more sense that way.
I added a phandle to the dtb node and updated the code accordingly.

[manu]

sys/dev/dwc/if_dwc_cvitek.c

80

What do you mean ? You're not supposed to modify the dtb but follow the bindings.

[bnovkov]

Remove redundant initialization steps.

[bnovkov]

sys/dev/dwc/if_dwc_cvitek.c

80

The bindings required a few smaller interventions in other places to make things work, and in the previous diff I just added a syscon phandle reference to avoid the hacky way of searching for a syscon.

However, after some more digging, it turned out that the steps in the init method were not required at all, the driver works without the clock-related steps fomr the init procedure.

[manu]

sys/dev/dwc/if_dwc_cvitek.c

80

Probably because u-boot have init the controller already, it's likely needed.

[bnovkov]

sys/dev/dwc/if_dwc_cvitek.c

80

sorry, managed to miss your comment.
So the DTS lists the stmmaceth clock as a 'fixed-clock', I guess this is why the driver works without explicitly enabling the clock in probe.

[bnovkov]

@manu are there any leftover issues here that you'd like to see addressed? I'm not entirely sure what is blocking this review at the moment.

[manu]

sys/dev/dwc/if_dwc_cvitek.c

74

That's a bit weird but ok, not the first time we see stuff like this :)

80

Ok, make sense then.