netdev - Re: [PATCH net-next 2/3] net: stmmac: xgmac: Correct supported speed modes

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Message-ID: <4df7133e-5dcd-4d3d-9a58-d09ad5fd7ec3@altera.com>
Date: Thu, 24 Jul 2025 21:48:29 +0530
From: "G Thomas, Rohan" <rohan.g.thomas@...era.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Romain Gantois <romain.gantois@...tlin.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Matthew Gerlach <matthew.gerlach@...era.com>
Subject: Re: [PATCH net-next 2/3] net: stmmac: xgmac: Correct supported speed
 modes

On 7/17/2025 5:17 PM, Serge Semin wrote:
> DW XGMAC IP-core of v2.x and older don't support 10/100Mbps modes
> neither in the XGMII nor in the GMII interfaces. That's why I dropped
> the 10/100Mbps link capabilities retaining 1G, 2.5G and 10G speeds
> only (the only speeds supported for DW XGMAC 1.20a/2.11a Tx in the
> MAC_Tx_Configuration.SS register field). Although I should have
> dropped the MAC_5000FD too since it has been supported since v3.0
> IP-core version. My bad.(
> 
> Starting from DW XGMAC v3.00a IP-core the list of the supported speeds
> has been extended to: 10/100Mbps (MII), 1G/2.5G (GMII), 2.5G/5G/10G
> (XGMII). Thus the more appropriate fix here should take into account
> the IP-core version. Like this:
> 	if (dma_cap->mbps_1000 && MAC_Version.SNPSVER >= 0x30)
> 		dma_cap->mbps_10_100 = 1;
> 
> Then you can use the mbps_1000 and mbps_10_100 flags to set the proper
> MAC-capabilities to hw->link.caps in the dwxgmac2_setup() method. I
> would have added the XGMII 2.5G/5G MAC-capabilities setting up to the
> dwxgmac2_setup() method too for the v3.x IP-cores and newer.

Hi Serge,

 From the databook, I noticed the condition:
(DWCXG_XGMII_GMII == 1) && <DWC-XGMAC-V2_20 feature authorized>
which seems to suggest that 10/100 Mbps support was introduced starting
from version 2.20.

Am I interpreting this correctly, or is this feature only fully
supported from v3.00 onwards.

Best Regards,
Rohan