Re: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Thu, Feb 20, 2025 at 11:30:52AM +0000, Gupta, Suraj wrote:
> Sorry for picking up this thread after long time, we checked
> internally with AMD IP and hardware experts and it is true that you
> can use this MAC and PCS to operate at 1G and 2.5G both. It is also
> possible to switch between these two speeds dynamically using
> external GT and/or if an external RTL logic is implemented in the
> FPGA. That will include some GPIO or register based selections to
> change the clock and configurations to switch between the speeds.
> Our current solution does not support this and is meant for a
> static speed selection only.

Thanks for getting back on this.

Okay, so it's a synthesis option, where that may be one of:

1. SGMII/1000base-X only
2. 2500base-X only
3. dynamically switching between (1) and (2).

> We'll use MAC ability register to detect if MAC is configured for
> 2.5G. Will it be fine to advertise both 1G and 2.5G in that case?

Please document in a comment that the above are synthesis options,
and that dynamically changing between them is possible but not
implemented by the driver. Note that should anyone use axienet for
SFP modules, then (1) is essentially the base functionality, (2) is
very limiting, and (3) would be best.

Not only will one want to limit the MAC capabilities, but also the
supported interface modes. As it's been so long since the patch was
posted, I don't remember whether it did that or not.

Thanks.

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