netdev - Re: [PATCH net-next 0/3] net: stmmac: phylink PCS conversion part 3 (dodgy stuff)

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Message-ID: <aQiBjYNtJks2/mrw@oss.qualcomm.com>
Date: Mon, 3 Nov 2025 15:48:53 +0530
From: Mohd Ayaan Anwar <mohd.anwar@....qualcomm.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Alexis Lothoré <alexis.lothore@...tlin.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        Boon Khai Ng <boon.khai.ng@...era.com>,
        Daniel Machon <daniel.machon@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Furong Xu <0x1207@...il.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "Jan Petrous (OSS)" <jan.petrous@....nxp.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        Vladimir Oltean <olteanv@...il.com>,
        Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH net-next 0/3] net: stmmac: phylink PCS conversion part 3
 (dodgy stuff)

On Mon, Nov 03, 2025 at 09:52:38AM +0000, Russell King (Oracle) wrote:
> On Mon, Nov 03, 2025 at 02:28:24PM +0530, Mohd Ayaan Anwar wrote:
> > On Thu, Oct 30, 2025 at 03:22:12PM +0000, Russell King (Oracle) wrote:
> > > On Thu, Oct 30, 2025 at 03:19:27PM +0000, Russell King (Oracle) wrote:
> > > > > 
> > > > > This is probably fine since Bit(9) is self-clearing and its value just
> > > > > after this is 0x00041000.
> > > > 
> > > > Yes, and bit 9 doesn't need to be set at all. SGMII isn't "negotiation"
> > > > but the PHY says to the MAC "this is how I'm operating" and the MAC says
> > > > "okay". Nothing more.
> > > > 
> > > > I'm afraid the presence of snps,ps-speed, this disrupts the test.
> > > 
> > > Note also that testing a 10M link, 100M, 1G and finally 100M again in
> > > that order would also be interesting given my question about the RGMII
> > > register changes that configure_sgmii does.
> > > 
> > 
> > Despite several attempts, I couldn't get 10M to work. There is a link-up
> > but the data path is broken. I checked the net-next tip and it's broken
> > there as well.
> > 
> > Oddly enough, configure_sgmii is called with its speed argument set to
> > 1000:
> > [   12.305488] qcom-ethqos 23040000.ethernet eth0: phy link up sgmii/10Mbps/Half/pause/off/nolpi
> > [   12.315233] qcom-ethqos 23040000.ethernet eth0: major config, requested phy/sgmii
> > [   12.322965] qcom-ethqos 23040000.ethernet eth0: interface sgmii inband modes: pcs=00 phy=03
> > [   12.331586] qcom-ethqos 23040000.ethernet eth0: major config, active phy/outband/sgmii
> > [   12.339738] qcom-ethqos 23040000.ethernet eth0: phylink_mac_config: mode=phy/sgmii/pause adv=0000000,00000000,00000000,00000000 pause=00
> > [   12.355113] qcom-ethqos 23040000.ethernet eth0: ethqos_configure_sgmii : Speed = 1000
> > [   12.363196] qcom-ethqos 23040000.ethernet eth0: Link is Up - 10Mbps/Half - flow control off
> 
> If you have "rate matching" enabled (signified by "pause" in the mode=
> part of phylink_mac_config), then the MAC gets told the maximum speed for
> the PHY interface, which for Cisco SGMII is 1G. This is intentional to
> support PHYs that _really_ do use rate matching. Your PHY isn't using it,
> and rate matching for SGMII is pointless.
> 
> Please re-run testing with phy-mode = "sgmii" which you've tested
> before without your rate-matching patch to the PHY driver, so the
> system knows the _correct_ parameters for these speeds.
> 
Sorry, I forgot to mention that all the recent testing is being done on
QCS9100 Ride R3 which has the AQR115C PHY.

My rate-matching patch was for IQ8 which has the QCA808X PHY. I am
putting its testing on hold until we sort everything out on QCS9100
first.

So, for AQR115C, what should be the way forward? It has support for rate
matching. For 10M should I remove its .get_rate_matching callback?

	Ayaan

> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!