Re: Aquantia PHY in OCSGMII mode?

Alexander Wilhelm
2025-08-27T08:33:04Z

Am Wed, Aug 27, 2025 at 09:08:24AM +0100 schrieb Russell King (Oracle):
> On Wed, Aug 27, 2025 at 07:57:28AM +0200, Alexander Wilhelm wrote:
> > Hi Vladimir,
> >
> > One of our hardware engineers has looked into the issue with the 100M link and
> > found the following: the Aquantia AQR115 always uses 2500BASE-X (GMII) on the
> > host side. For both 1G and 100M operation, it enables pause rate adaptation.
> > However, our MAC only applies rate adaptation for 1G links. For 100M, it uses a
> > 10x symbol replication instead.
>
> This sounds like a misunderstanding, specifically:
>
> "our MAC only applies rate adaptation for 1G links. For 100M, it uses
> 10x symbol replication instead."
>
> It is the PHY that does rate adaption, so the MAC doesn't need to
> support other speeds. Therefore, if the PHY is using a 2.5Gbps link
> to the MAC with rate adaption for 100M, then the MAC needs to operate
> at that 2.5Gbps speed.
>
> You don't program the MAC differently depending on the media side
> speed, unlike when rate adaption is not being used.

You're right. The flow control with rate adaptation is controlled by PHY. The
MAC should remain on the 2.5Gbps speed. Therefore I wonder why it uses 10x
symbol repetition.

Best regards
Alexander Wilhelm