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

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Message-ID:
 <BL3PR12MB65716077E66F2141CC618DD9C9202@BL3PR12MB6571.namprd12.prod.outlook.com>
Date: Tue, 19 Nov 2024 10:28:48 +0000
From: "Gupta, Suraj" <Suraj.Gupta2@....com>
To: Russell King <linux@...linux.org.uk>, Sean Anderson
	<sean.anderson@...ux.dev>
CC: "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"Simek, Michal" <michal.simek@....com>, "Pandey, Radhey Shyam"
	<radhey.shyam.pandey@....com>, "horms@...nel.org" <horms@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "git (AMD-Xilinx)" <git@....com>, "Katakam,
 Harini" <harini.katakam@....com>
Subject: RE: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC



> -----Original Message-----
> From: Russell King <linux@...linux.org.uk>
> Sent: Monday, November 18, 2024 9:39 PM
> To: Sean Anderson <sean.anderson@...ux.dev>
> Cc: Gupta, Suraj <Suraj.Gupta2@....com>; andrew+netdev@...n.ch;
> davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> pabeni@...hat.com; Simek, Michal <michal.simek@....com>; Pandey, Radhey
> Shyam <radhey.shyam.pandey@....com>; horms@...nel.org;
> netdev@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; git (AMD-Xilinx) <git@....com>; Katakam, Harini
> <harini.katakam@....com>
> Subject: Re: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC
> 
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
> 
> 
> 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.
> 
As mentioned in IP PG (https://docs.amd.com/r/en-US/pg051-tri-mode-eth-mac/Ethernet-Overview#:~:text=Typical%20Ethernet%20Architecture-,MAC,-For%2010/100), it's limitation in MAC also.

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