linux-kernel - Re: [PATCH 09/15] net: hbl_en: add habanalabs Ethernet driver

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Message-ID: <1baf52ff-d3ce-4d3f-9655-46a1a919119b@lunn.ch>
Date: Wed, 26 Jun 2024 16:13:55 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Omer Shpigelman <oshpigelman@...ana.ai>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"ogabbay@...nel.org" <ogabbay@...nel.org>,
	Zvika Yehudai <zyehudai@...ana.ai>
Subject: Re: [PATCH 09/15] net: hbl_en: add habanalabs Ethernet driver

> Here is the output:
> $ ethtool eth0
> Settings for eth0:
> 	Supported ports: [ FIBRE	 Backplane ]
> 	Supported link modes:   100000baseKR4/Full
> 	                        100000baseSR4/Full
> 	                        100000baseCR4/Full
> 	                        100000baseLR4_ER4/Full
> 	Supported pause frame use: Symmetric
> 	Supports auto-negotiation: Yes
> 	Supported FEC modes: Not reported
> 	Advertised link modes:  100000baseKR4/Full
> 	                        100000baseSR4/Full
> 	                        100000baseCR4/Full
> 	                        100000baseLR4_ER4/Full
> 	Advertised pause frame use: Symmetric
> 	Advertised auto-negotiation: Yes
> 	Advertised FEC modes: Not reported
> 	Link partner advertised link modes:  Not reported
> 	Link partner advertised pause frame use: No
> 	Link partner advertised auto-negotiation: Yes
> 	Link partner advertised FEC modes: Not reported
> 	Speed: 100000Mb/s
> 	Duplex: Full
> 	Auto-negotiation: on
> 
> There are few points to mention:
> 1. We don't allow to modify the advertised link modes so by definition the
>    advertised ones are a copy of the supported ones.

So there is no way to ask it use to use 100000baseCR4/Full, for
example? You would normally change the advertised modes to just that
one link mode, and then it has no choice. It either uses
100000baseCR4/Full, or it does not establish a link.

Also, my experience with slower modules is that one supporting
2500BaseX can also support 1000BaseX. However, there is no auto-neg
defined for speeds, just pause. So if the link peer only supports
1000BaseX, you don't get link. What you typically see is:

$ ethtool eth0
Settings for eth0:
 	Supported ports: [ FIBRE	 Backplane ]
 	Supported link modes:   1000baseX
 	                        2500baseX
 	Supported pause frame use: Symmetric
 	Supports auto-negotiation: Yes
 	Supported FEC modes: Not reported
 	Advertised link modes:  2500baseX
 	Advertised pause frame use: Symmetric

and then you use ethtool to change advertising to 1000baseX and then
you get link. Can these modules support slower speeds?

> 2. Reading the peer advertised link modes is not supported so we don't
>    report them (similarly to some other vendors).

Not supported by your firmware? Or not supported by the modules?

    Andrew