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

[Gupta, Suraj]

> -----Original Message-----
> From: Russell King <linux at armlinux.org.uk>
> Sent: Monday, November 18, 2024 9:39 PM
> To: Sean Anderson <sean.anderson at linux.dev>
> Cc: Gupta, Suraj <Suraj.Gupta2 at amd.com>; andrew+netdev at lunn.ch;
> davem at davemloft.net; edumazet at google.com; kuba at kernel.org;
> pabeni at redhat.com; Simek, Michal <michal.simek at amd.com>; Pandey, Radhey
> Shyam <radhey.shyam.pandey at amd.com>; horms at kernel.org;
> netdev at vger.kernel.org; linux-arm-kernel at lists.infradead.org; linux-
> kernel at vger.kernel.org; git (AMD-Xilinx) <git at amd.com>; Katakam, Harini
> <harini.katakam at amd.com>
> Subject: Re: [PATCH net-next 2/2] net: axienet: Add support for AXI 2.5G MAC
> 
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> 
> 
> 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 at amd.com>
> > >> Signed-off-by: Harini Katakam <harini.katakam at amd.com>
> > >> Signed-off-by: Suraj Gupta <suraj.gupta2 at amd.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.

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