netdev - Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal delay configuration

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Date:   Thu, 13 Jan 2022 07:32:13 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        martin.blumenstingl@...glemail.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, hkallweit1@...il.com,
        David Miller <davem@...emloft.net>, kuba@...nel.org,
        netdev <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal
 delay configuration

On 2022-01-12 19:25, Tim Harvey wrote:
> On Wed, Jan 12, 2022 at 5:46 AM Russell King (Oracle)
> <linux@...linux.org.uk> wrote:
>> 
>> On Tue, Jan 11, 2022 at 11:12:33AM -0800, Tim Harvey wrote:
>> > I added a debug statement in xway_gphy_rgmii_init and here you can see
>> > it gets called 'before' the link comes up from the NIC on a board that
>> > has a cable plugged in at power-on. I can tell from testing that the
>> > rx_delay/tx_delay set in xway_gphy_rgmii_init does not actually take
>> > effect unless I then bring the link down and up again manually as you
>> > indicate.
>> >
>> > # dmesg | egrep "xway|nicvf"
>> > [    6.855971] xway_gphy_rgmii_init mdio_thunder MDI_MIICTRL:0xb100
>> > rx_delay=1500 tx_delay=500
>> > [    6.999651] nicvf, ver 1.0
>> > [    7.002478] nicvf 0000:05:00.1: Adding to iommu group 7
>> > [    7.007785] nicvf 0000:05:00.1: enabling device (0004 -> 0006)
>> > [    7.053189] nicvf 0000:05:00.2: Adding to iommu group 8
>> > [    7.058511] nicvf 0000:05:00.2: enabling device (0004 -> 0006)
>> > [   11.044616] nicvf 0000:05:00.2 eth1: Link is Up 1000 Mbps Full duplex
>> 
>> Does the kernel message about the link coming up reflect what is going
>> on physically with the link though?
>> 
>> If a network interface is down, it's entirely possible that the link 
>> is
>> already established at the hardware level, buit the "Link is Up" 
>> message
>> gets reported when the network interface is later brought up. So,
>> debugging this by looking at the kernel messages is unreliable.
>> 
> 
> Russell,
> 
> You are correct... the link doesn't come up at that point its already
> linked. So we need to force a reset or an auto negotiation reset after
> modifying the delays.
> 
> Tim

Setting BMCR_ANRESTART would work, but only if BMCR_ANENABLE is also or
already set. Otherwise BMCR_ANRESTART has no effect (see the note in the
datasheet).

This is the reason why I came up with the idea of BMCR_PDOWN.

Personally I would have no problem with setting BMCR_ANRESTART and
BMCR_ANENABLE, but it would possibly change the existing configuration
if (e.g. by the bootloader) aneg should be disabled.

Martin