netdev - Re: Information on DSA driver initialization

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Date:   Thu, 12 Mar 2020 18:38:24 -0400
From:   Sriram Chadalavada <sriram.chadalavada@...dleap.ca>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org
Subject: Re: Information on DSA driver initialization

Hi Andrew,
   Thank you for your response.

  Yes. There are patches applied.  I did scatter printks/pr_info but
don't see anything yet from the Marvell 6176 switch without
CONFIG_NET_DSA_LEGACY enabled.

    One question I have is if CONFIG_NET_DSA_LEGACY is NOT selected,
what in the 4.19 kernel takes over the function of dsa_probe function
in net/dsa/legacy.c and mv88e6xxx_drv_probe in
drivers/net/dsa/mv88e6xxx/chip.c ?

- Sriram




On Thu, Mar 5, 2020 at 5:51 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Thu, Mar 05, 2020 at 05:24:47PM -0500, Sriram Chadalavada wrote:
> > Is there information in kernel documentation or elsewhere about DSA
> > initialization process starting from the device tree parse to the
> > Marvell switch being detected?
> >
> > The specific problem I'm facing is that while I see this:
> > root@...ub:/# dmesg | grep igb
> > [ 1.314324] igb: Intel(R) Gigabit Ethernet Network Driver - version 5.4.0-k
> > [ 1.314332] igb: Copyright (c) 2007-2014 Intel Corporation.
> > [ 1.314679] igb 0000:03:00.0: enabling device (0140 -> 0142)
> > [ 1.343926] igb 0000:03:00.0: added PHC on eth0
> > [ 1.343938] igb 0000:03:00.0: Intel(R) Gigabit Ethernet Network Connection
> > [ 1.343949] igb 0000:03:00.0: eth0: (PCIe:2.5Gb/s:Width x1) c4:48:38:00:63:eb
> > [ 1.344019] igb 0000:03:00.0: eth0: PBA No: 000300-000
> > [ 1.344030] igb 0000:03:00.0: Using MSI-X interrupts. 4 rx queue(s), 4
> > tx queue(s)
> > [ 1.344464] libphy: igb_enet_mii_bus: probed
> >
> > I do NOT see this in the log:
> > [ 1.505474] libphy: mdiobus_find: mii bus [igb_enet_mii_bus] found
> > [ 1.645075] igb 0000:03:00.0 eth0: [0]: detected a Marvell 88E6176 switch
> > [ 24.341748] igb 0000:03:00.0 eth0: igb_enet_mii_probe starts
> > [ 24.344928] igb 0000:03:00.0 eth0: igb: eth0 NIC Link is Up 1000 Mbps
> > Full Duplex, Flow Control: RX/TX
> >
> > Any suggestions/speculations what may be going on here?
>
> I think you have some patches applied here, because i don't think igb
> supports linux mdio. It has its own implementation.
>
> Assuming that is what you have, the probe of the switch normally fails
> the first time. Generally, the mdio bus is registered before the
> network interface. So when the switch tried to lookup the ethernet
> interface, it does not exist. -EPROBE_DEFFER is returned. The core
> will then try again, by which time the interfaces does exist.
>
> You probably want to scatter some printk() in the code to see what is
> happening.
>
>         Andrew