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

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Date: Mon, 3 Jun 2024 16:45:30 +0530
From: Sneh Shah <quic_snehshah@...cinc.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>,
        Andrew Lunn
	<andrew@...n.ch>
CC: 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 5/30/2024 1:43 AM, Russell King (Oracle) wrote:
> 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!

Do we mean SGMII autoneg by SGMII inband signalling? Our hardware doesn't
support autoneg for 2.5G mode in SGMII.
>