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

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Message-ID: <72ded972-cd16-4124-84af-8d8ddad049f0@linux.dev>
Date: Tue, 19 Nov 2024 10:26:52 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Andrew Lunn <andrew@...n.ch>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
 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 11/18/24 20:35, Andrew Lunn wrote:
> 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.
> 
> 
> And can the PCS change between these modes? It is pretty typical to
> use SGMII for 10/100/1G and then swap to 2500BaseX for 2.5G.

Not AFAIK. There's only a bit for switching between 1000Base-X and
SGMII. 2500Base-X is selected at synthesis time, and AIUI the serdes
settings are different.

--Sean