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

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Message-ID: <657764fd-68a1-4826-b832-3bda91a0c13b@linux.dev>
Date: Mon, 18 Nov 2024 11:00:22 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: "Russell King (Oracle)" <linux@...linux.org.uk>,
 Suraj Gupta <suraj.gupta2@....com>
Cc: 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 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.

--Sean

> Normally, max speeds can be limited using phylink_limit_mac_speed()
> which will clear any MAC capabilities for speeds faster than the
> speed specified.
>