Message-ID: <20250211143209.74f84a10@kmaincent-XPS-13-7390>
Date: Tue, 11 Feb 2025 14:32:09 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
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Subject: Re: [PATCH net-next 03/13] net: phy: Introduce PHY ports
 representation

On Fri,  7 Feb 2025 23:36:22 +0100
Maxime Chevallier <maxime.chevallier@...tlin.com> wrote:

> Ethernet provides a wide variety of layer 1 protocols and standards for
> data transmission. The front-facing ports of an interface have their own
> complexity and configurability.
> 
> Introduce a representation of these front-facing ports. The current code
> is minimalistic and only support ports controlled by PHY devices, but
> the plan is to extend that to SFP as well as raw Ethernet MACs that
> don't use PHY devices.
> 
> This minimal port representation allows describing the media and number
> of lanes of a port. From that information, we can derive the linkmodes
> usable on the port, which can be used to limit the capabilities of an
> interface.
> 
> For now, the port lanes and medium is derived from devicetree, defined
> by the PHY driver, or populated with default values (as we assume that
> all PHYs expose at least one port).
> 
> The typical example is 100M ethernet. 100BaseT can work using only 2
> lanes on a Cat 5 cables. However, in the situation where a 10/100/1000
> capable PHY is wired to its RJ45 port through 2 lanes only, we have no
> way of detecting that. The "max-speed" DT property can be used, but a
> more accurate representation can be used :
> 
> mdi {
> 	port@0 {
> 		media = "BaseT";
> 		lanes = <2>;
> 	};
> };
> 
> From that information, we can derive the max speed reachable on the
> port.
> 
> Another benefit of having that is to avoid vendor-specific DT properties
> (micrel,fiber-mode or ti,fiber-mode).
> 
> This basic representation is meant to be expanded, by the introduction
> of port ops, userspace listing of ports, and support for multi-port
> devices.

This patch is tackling the support of ports only for the PHY API. Keeping in
mind that this port abstraction support will also be of interest to the NICs.
Isn't it preferable to handle port in a standalone API?

With net drivers having PHY managed by the firmware or DSA, there is no linux
description of their PHYs. On that case, if we want to use port abstraction,
what is the best? Register a virtual phy_device to use the abstraction port or
use the port abstraction API directly which meant that it is not related to any
PHY?

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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