netdev - Re: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC

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Message-ID: <Zztml-Te38P3M7cM@shell.armlinux.org.uk>
Date: Mon, 18 Nov 2024 16:08:55 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Suraj Gupta <suraj.gupta2@....com>, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, michal.simek@....com,
	radhey.shyam.pandey@....com, horms@...nel.org,
	netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, git@....com, harini.katakam@....com
Subject: Re: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC

On Mon, Nov 18, 2024 at 11:00:22AM -0500, Sean Anderson wrote:
> On 11/18/24 10:56, Russell King (Oracle) wrote:
> > On Mon, Nov 18, 2024 at 01:48:22PM +0530, Suraj Gupta wrote:
> >> Add AXI 2.5G MAC support, which is an incremental speed upgrade
> >> of AXI 1G MAC and supports 2.5G speed only. "max-speed" DT property
> >> is used in driver to distinguish 1G and 2.5G MACs of AXI 1G/2.5G IP.
> >> If max-speed property is missing, 1G is assumed to support backward
> >> compatibility.
> >> 
> >> Co-developed-by: Harini Katakam <harini.katakam@....com>
> >> Signed-off-by: Harini Katakam <harini.katakam@....com>
> >> Signed-off-by: Suraj Gupta <suraj.gupta2@....com>
> >> ---
> > 
> > ...
> > 
> >> -	lp->phylink_config.mac_capabilities = MAC_SYM_PAUSE | MAC_ASYM_PAUSE |
> >> -		MAC_10FD | MAC_100FD | MAC_1000FD;
> >> +	lp->phylink_config.mac_capabilities = MAC_SYM_PAUSE | MAC_ASYM_PAUSE;
> >> +
> >> +	/* Set MAC capabilities based on MAC type */
> >> +	if (lp->max_speed == SPEED_1000)
> >> +		lp->phylink_config.mac_capabilities |= MAC_10FD | MAC_100FD | MAC_1000FD;
> >> +	else
> >> +		lp->phylink_config.mac_capabilities |= MAC_2500FD;
> > 
> > The MAC can only operate at (10M, 100M, 1G) _or_ 2.5G ?
> 
> It's a PCS limitation. It either does (1000Base-X and/or SGMII) OR
> (2500Base-X). The MAC itself doesn't have this limitation AFAIK.

That means the patch is definitely wrong, and the proposed DT
change is also wrong.

If it's a limitation of the PCS, that limitation should be applied
via the PCS's .pcs_validate() method, not at the MAC level.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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