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

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Message-ID: <ZleMdFsmQzXGp1GM@shell.armlinux.org.uk>
Date: Wed, 29 May 2024 21:13:40 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Sneh Shah <quic_snehshah@...cinc.com>,
	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

On Wed, May 29, 2024 at 04:28:16PM +0200, Andrew Lunn wrote:
> > 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?

I really hope the hardware isn't using any SGMII inband signalling
at 2.5G speeds. Other devices explicitly state that SGMII inband
signalling while operating the elevated 2.5G speed is *not* supported!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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