Re: [PATCH net-next v2 0/5] TSN auto negotiation between 1G and 2.5G

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Cc: "Andrew Lunn" <andrew@lunn.ch>,
	"Rajneesh Bhardwaj" <irenic.rajneesh@gmail.com>,
	"David E Box" <david.e.box@linux.intel.com>,
	"Hans de Goede" <hdegoede@redhat.com>,
	"Mark Gross" <markgross@kernel.org>,
	"Jose Abreu" <Jose.Abreu@synopsys.com>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Marek Behún" <kabel@kernel.org>,
	"Jean Delvare" <jdelvare@suse.com>,
	"Guenter Roeck" <linux@roeck-us.net>,
	"Giuseppe Cavallaro" <peppe.cavallaro@st.com>,
	"Alexandre Torgue" <alexandre.torgue@foss.st.com>,
	"Jose Abreu" <joabreu@synopsys.com>,
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	"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
	"Revanth Kumar Uppala" <ruppala@nvidia.com>,
	"Shenwei Wang" <shenwei.wang@nxp.com>,
	"Andrey Konovalov" <andrey.konovalov@linaro.org>,
	"Jochen Henneberg" <jh@henneberg-systemdesign.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
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	platform-driver-x86@vger.kernel.org, linux-hwmon@vger.kernel.org,
	bpf@vger.kernel.org, "Voon Wei Feng" <weifeng.voon@intel.com>,
	"Tan Tee Min" <tee.min.tan@linux.intel.com>,
	"Michael Sit Wei Hong" <michael.wei.hong.sit@intel.com>,
	"Lai Peter Jun Ann" <jun.ann.lai@intel.com>
Subject: Re: [PATCH net-next v2 0/5] TSN auto negotiation between 1G and 2.5G
Date: Thu, 21 Sep 2023 14:39:56 +0100	[thread overview]
Message-ID: <ZQxHrPS5C13SfTfA@shell.armlinux.org.uk> (raw)
In-Reply-To: <f9b21a9d-4ae2-1f91-b621-2e27f746f661@linux.intel.com>

On Thu, Sep 21, 2023 at 08:25:05PM +0800, Choong Yong Liang wrote:
> 
> 
> On 4/8/2023 8:04 pm, Andrew Lunn wrote:
> > On Fri, Aug 04, 2023 at 04:45:22PM +0800, Choong Yong Liang wrote:
> > > Intel platforms’ integrated Gigabit Ethernet controllers support
> > > 2.5Gbps mode statically using BIOS programming. In the current
> > > implementation, the BIOS menu provides an option to select between
> > > 10/100/1000Mbps and 2.5Gbps modes. Based on the selection, the BIOS
> > > programs the Phase Lock Loop (PLL) registers. The BIOS also read the
> > > TSN lane registers from Flexible I/O Adapter (FIA) block and provided
> > > 10/100/1000Mbps/2.5Gbps information to the stmmac driver. But
> > > auto-negotiation between 10/100/1000Mbps and 2.5Gbps is not allowed.
> > > The new proposal is to support auto-negotiation between 10/100/1000Mbps
> > > and 2.5Gbps . Auto-negotiation between 10, 100, 1000Mbps will use
> > > in-band auto negotiation. Auto-negotiation between 10/100/1000Mbps and
> > > 2.5Gbps will work as the following proposed flow, the stmmac driver reads
> > > the PHY link status registers then identifies the negotiated speed.
> > > Based on the speed stmmac driver will identify TSN lane registers from
> > > FIA then send IPC command to the Power Management controller (PMC)
> > > through PMC driver/API. PMC will act as a proxy to programs the
> > > PLL registers.
> > 
> > Have you considered using out of band for all link modes? You might
> > end up with a cleaner architecture, and not need any phylink/phylib
> > hacks.
> > 
> > 	Andrew
> Hi Andrew,
> 
> After conducting a comprehensive study, it seems that implementing
> out-of-band for all link modes might not be feasible. I may have missed some
> key aspects during my analysis.

You need to provide details of why you think it's not feasible, because
you're making those reading your message have to guess.

We _do_ have cases where this is already supported. The DM7052 SFP
module for example has a BCM84881 PHY on board that has no in-band
support, so always has to use out-of-band. This module supports 10G,
5G, 2.5G, 1G, 100M and 10M speeds. It switches its interface between
10G, 2500base-X and SGMII mode. It's been supported in Linux for a
while with MAC/PCS that implement phylink _correctly_.

I wouldn't call stmmac a proper phylink implementation, especially
when it comes to switching between different interfaces.

My attempt at starting to clean up the stmmac code was thwarted by
niggly review comments (over whether %u or %d should be used to print
a _signed integer_ that stmmac stupidly implicitly casts to an unsigned
integer. That lead me to decide that stmmac was beyond being cleaned
up, so I junked the large patch set of improvements that I had - along
with multiple issues that I had found in the driver.

Someone else needs to sort stmmac out, and I suspect that may be a
pre-requisit for your changes so that stmmac operates _correctly_ with
phylink.

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

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