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

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Message-ID: <b192c96a-2989-4bdf-ba4f-8b7bcfd09cfa@lunn.ch>
Date: Mon, 14 Jul 2025 15:42:43 +0200
From: Andrew Lunn <andrew@...n.ch>
To: rohan.g.thomas@...era.com
Cc: 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>,
	Serge Semin <fancer.lancer@...il.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 Mon, Jul 14, 2025 at 03:59:18PM +0800, Rohan G Thomas via B4 Relay wrote:
> From: Rohan G Thomas <rohan.g.thomas@...era.com>
> 
> Correct supported speed modes as per the XGMAC databook.
> Commit 9cb54af214a7 ("net: stmmac: Fix IP-cores specific
> MAC capabilities") removes support for 10M, 100M and
> 1000HD. 1000HD is not supported by XGMAC IP, but it does
> support 10M and 100M FD mode, and it also supports 10M and
> 100M HD mode if the HDSEL bit is set in the MAC_HW_FEATURE0
> reg. This commit adds support for 10M and 100M speed modes
> for XGMAC IP.

> +++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
> @@ -405,6 +405,7 @@ static int dwxgmac2_get_hw_feature(void __iomem *ioaddr,
>  	dma_cap->sma_mdio = (hw_cap & XGMAC_HWFEAT_SMASEL) >> 5;
>  	dma_cap->vlhash = (hw_cap & XGMAC_HWFEAT_VLHASH) >> 4;
>  	dma_cap->half_duplex = (hw_cap & XGMAC_HWFEAT_HDSEL) >> 3;
> +	dma_cap->mbps_10_100 = (hw_cap & XGMAC_HWFEAT_GMIISEL) >> 1;

The commit message does not mention this change.

What does XGMAC_HWFEAT_GMIISEL mean? That a SERDES style interface is
not being used? Could that be why Serge removed these speeds? He was
looking at systems with a SERDES, and they don't support slower
speeds?

	Andrew