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

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Message-ID: <tcebsuesjejtk3vmzx77yuo7zil2xciucnnrakubrslwvnndas@utvi4r7ob3xa>
Date: Thu, 24 Jul 2025 20:56:06 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: "G Thomas, Rohan" <rohan.g.thomas@...era.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

Hi Rohan

On Thu, Jul 24, 2025 at 09:48:29PM +0530, G Thomas, Rohan wrote:
> 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.

Hm. Interesting discovery. I've got only DW XGMAC v1.20a, v2.11a,
v3.01a and v3.20a databooks at hands. So I can't prove for sure your
inference. But the DW XGMAC v3.01a doc indeed states that
DWCXG_FDUPLX_ONLY parameter is enabled if:
(DWCXG_XGMII_GMII == 1) && <DWC-XGMAC-V2_20 feature authorized>
which implies that the parameter was originally introduced in v2.20a
IP-core.

So to speak you might be right. Perhaps it will be more correct to set
dma_cap->mbps_10_100 for v2.20a (SNPSVER = 0x22) IP-cores too
especially seeing another parameter DWCXG_MII_SUPPORT depends on
SNPS_RSVDPARAM_16 which also depends on DWC-XGMAC-V2_20.

-Serge(y)

> 
> Best Regards,
> Rohan