Re: [PATCH net-next] net: renesas: rswitch: cleanup max_speed setting

[Andrew Lunn <andrew@lunn.ch>]

On Mon, Feb 03, 2025 at 06:09:41PM +0100, Nikita Yushchenko wrote:
> It was observed on spider board that with upstream kernel, PHY
> auto-negotiation takes almost 1 second longer than with renesas BSP
> kernel. This was tracked down to upstream kernel allowing more PHY modes
> than renesas BSP kernel.
> 
> To avoid that effect when possible, always set max_speed to not more
> than phy_interface allows.

Please could you provide more information about the hardware. Is the
PHY more capable than the MAC?

When you have multi Gigi PHYs, the phy-mode is often taken to be the
starting point. But when the PHY has negotiated a link, it will tell
the MAC what PHY mode it needs to swap to, e.g from SGMII to
2500BaseX, etc.

You should only need max-speed when you have a PHY which can do more
than the MAC.

Also, phylink handles this a lot better than phylib. So you might want
to change rswitch to phylink, especially if you have link speeds > 1G.

	Andrew