linux-kernel - Re: [PATCH net-next] net: stmmac: dwmac-qcom-ethqos: Add support for 2.5G SGMII

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Date: Wed, 29 May 2024 16:28:16 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Sneh Shah <quic_snehshah@...cinc.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
	Andrew Halaney <ahalaney@...hat.com>, Vinod Koul <vkoul@...nel.org>,
	Bhupesh Sharma <bhupesh.sharma@...aro.org>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"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>, netdev@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...cinc.com
Subject: Re: [PATCH net-next] net: stmmac: dwmac-qcom-ethqos: Add support for
 2.5G SGMII

> Qualcomm ethernet HW supports 2.5G speed in overclocked SGMII mode.
> we internally term it as OCSGMII.

So it still does SGMII inband signalling? Not 2500BaseX signalling? It
is not actually compatible with 2500BaseX?

> End goal of these patches is to enable SGMII with 2.5G speed support.
> The patch in these series enabled up SGMII with 2.5 for cases where we
> don't have external phy. ( mac-to-mac connectivity)

So the other end needs to be an over clocked SGMII MAC, not 2500BaseX?

> The new patch posted extends this for the case when the MAC has an
> external phy connected. ( hence we are advertising fr 2.5G speed by adding
> 2500BASEX as supported interface in phylink)

And i assume it does not actually work against a true 2500BaseX
device, because it is doing SGMII inband signalling?
 
Hence Russell frustration with the whole 2.5G mess....

      Andrew