Date:   Wed, 29 Apr 2020 09:21:58 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Robert Hancock <hancock@...systems.ca>
Cc:     Andre Przywara <andre.przywara@....com>,
        Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        Michal Simek <michal.simek@...inx.com>,
        linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: Xilinx axienet 1000BaseX support

On Tue, Apr 28, 2020 at 05:51:58PM -0600, Robert Hancock wrote:
> On 2020-04-28 5:01 p.m., Russell King - ARM Linux admin wrote:
> > On Tue, Apr 28, 2020 at 03:59:45PM -0600, Robert Hancock wrote:
> > > On 2020-04-22 1:51 a.m., Russell King - ARM Linux admin wrote:
> > > > On Tue, Apr 21, 2020 at 07:45:47PM -0600, Robert Hancock wrote:
> > > > > Hi Andre/Russell,
> > > > > 
> > > > > Just wondering where things got to with the changes for SGMII on Xilinx
> > > > > axienet that you were discussing (below)? I am looking into our Xilinx setup
> > > > > using 1000BaseX SFP and trying to get it working "properly" with newer
> > > > > kernels. My understanding is that the requirements for 1000BaseX and SGMII
> > > > > are somewhat similar. I gathered that SGMII was working somewhat already,
> > > > > but that not all link modes had been tested. However, it appears 1000BaseX
> > > > > is not yet working in the stock kernel.
> > > > > 
> > > > > The way I had this working before with a 4.19-based kernel was basically a
> > > > > hack to phylink to allow the Xilinx PCS/PMA PHY to be configured
> > > > > sufficiently as a PHY for it to work, and mostly ignored the link status of
> > > > > the SFP PHY itself, even though we were using in-band signalling mode with
> > > > > an SFP module. That was using this patch:
> > > > > 
> > > > > https://patchwork.ozlabs.org/project/netdev/patch/1559330285-30246-5-git-send-email-hancock@sedsystems.ca/
> > > > > 
> > > > > Of course, that's basically just a hack which I suspect mostly worked by
> > > > > luck. I see that there are some helpers that were added to phylink to allow
> > > > > setting PHY advertisements and reading PHY status from clause 22 PHY
> > > > > devices, so I'm guessing that is the way to go in this case? Something like:
> > > > > 
> > > > > axienet_mac_config: if using in-band mode, use
> > > > > phylink_mii_c22_pcs_set_advertisement to configure the Xilinx PHY.
> > > > > 
> > > > > axienet_mac_pcs_get_state: use phylink_mii_c22_pcs_get_state to get the MAC
> > > > > PCS state from the Xilinx PHY
> > > > > 
> > > > > axienet_mac_an_restart: if using in-band mode, use
> > > > > phylink_mii_c22_pcs_an_restart to restart autonegotiation on Xilinx PHY
> > > > > 
> > > > > To use those c22 functions, we need to find the mdio_device that's
> > > > > referenced by the phy-handle in the device tree - I guess we can just use
> > > > > some of the guts of of_phy_find_device to do that?
> > > > 
> > > > Please see the code for DPAA2 - it's changed slightly since I sent a
> > > > copy to the netdev mailing list, and it still isn't clear whether this
> > > > is the final approach (DPAA2 has some fun stuff such as several
> > > > different PHYs at address 0.) NXP basically didn't like the approach
> > > > I had in the patches I sent to netdev, we had a call, they presented
> > > > an alternative appraoch, I implemented it, then they decided my
> > > > original approach was the better solution for their situation.
> > > > 
> > > > See http://git.armlinux.org.uk/cgit/linux-arm.git/log/?h=cex7
> > > > 
> > > > specifically the patches from:
> > > > 
> > > >     "dpaa2-mac: add 1000BASE-X/SGMII PCS support"
> > > > 
> > > > through to:
> > > > 
> > > >     "net: phylink: add interface to configure clause 22 PCS PHY"
> > > > 
> > > > You may also need some of the patches further down in the net-queue
> > > > branch:
> > > > 
> > > >     "net: phylink: avoid mac_config calls"
> > > > 
> > > > through to:
> > > > 
> > > >     "net: phylink: rejig link state tracking"
> > > 
> > > I've been playing with this a bit on a 5.4 kernel with some of these patches
> > > backported. However, I'm running into something that my previous hacks for
> > > this basically dealt with as a side effect: when phylink_start is called,
> > > sfp_upstream_start gets called, an SFP module is detected,
> > > phylink_connect_phy gets called, but then it hits this condition and bails
> > > out, because we are using INBAND mode with 1000BaseX:
> > > 
> > > 	if (WARN_ON(pl->cfg_link_an_mode == MLO_AN_FIXED ||
> > > 		    (pl->cfg_link_an_mode == MLO_AN_INBAND &&
> > > 		     phy_interface_mode_is_8023z(interface))))
> > > 		return -EINVAL;
> > 
> > I'm expecting SGMII mode to be used when there's an external PHY as
> > that gives greatest flexibility (as it allows 10 and 100Mbps speeds
> > as well.)  From what I remember, these blocks support SGMII, so it
> > should just be a matter of adding that.
> 
> They do support SGMII, but unfortunately it's not a runtime configurable
> parameter, it's a synthesis-level parameter on the FPGA IP core so you have
> to pick one or the other for any given build. We want to be able to support
> various fiber module types as well, and my understanding is that at least
> some of those only do 1000BaseX, so that ends up being the standard in
> common that we are using.

1G Fibre modules are all 1000BaseX only.

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