Subject: Re: [PATCH net-next 2/2] net: phy: at803x: Support downstream SFP cage

From: "Russell King (Oracle)" <[email-masked]>
Date: Fri, 2 Jul 2021 00:12:53 +0100

On Wed, Jun 30, 2021 at 12:01:46PM -0600, Robert Hancock wrote:
> Add support for downstream SFP cages for AR8031 and AR8033. This is
> primarily intended for fiber modules or direct-attach cables, however
> copper modules which work in 1000Base-X mode may also function. Such
> modules are allowed with a warning.

Possibly that's because they default to 1000Base-X mode for
compatibility, but there are some (MikroTik S-RJ01) for example
where the PHY definitely is in SGMII mode and will negotiate
10/100Mbit on its media side which won't work with an AR803x.

> +	/* Some modules support 10G modes as well as others we support.
> +	 * Mask out non-supported modes so the correct interface is picked.
> +	 */
> +	linkmode_and(sfp_support, phy_support, sfp_support);

I think rather than relying on sfp_select_interface() complaining when
sfp_support is empty, do an explicit check here (phylink code
effectively does this via the phylink_validate() check.)

You'll then either be given SGMII or 1000BASE-X by
sfp_select_interface().

-- 
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