netdev - Re: [RFC net-next PATCH 16/16] net: sfp: Add quirk to ignore PHYs

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Date:   Tue, 5 Oct 2021 12:45:28 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [RFC net-next PATCH 16/16] net: sfp: Add quirk to ignore PHYs



On 10/5/21 6:33 AM, Russell King (Oracle) wrote:
> On Mon, Oct 04, 2021 at 03:15:27PM -0400, Sean Anderson wrote:
>> Some modules have something at SFP_PHY_ADDR which isn't a PHY. If we try to
>> probe it, we might attach genphy anyway if addresses 2 and 3 return
>> something other than all 1s. To avoid this, add a quirk for these modules
>> so that we do not probe their PHY.
>>
>> The particular module in this case is a Finisar SFP-GB-GE-T. This module is
>> also worked around in xgbe_phy_finisar_phy_quirks() by setting the support
>> manually. However, I do not believe that it has a PHY in the first place:
>>
>> $ i2cdump -y -r 0-31 $BUS 0x56 w
>>      0,8  1,9  2,a  3,b  4,c  5,d  6,e  7,f
>> 00: ff01 ff01 ff01 c20c 010c 01c0 0f00 0120
>> 08: fc48 000e ff78 0000 0000 0000 0000 00f0
>> 10: 7800 00bc 0000 401c 680c 0300 0000 0000
>> 18: ff41 0000 0a00 8890 0000 0000 0000 0000
>
> Actually, I think that is a PHY. It's byteswapped (which is normal using
> i2cdump in this way).The real contents of the registers are:
>
> 00: 01ff 01ff 01ff 0cc2 0c01 c001 000f 2001
> 08: 48fc 0e00 78ff 0000 0000 0000 0000 f000
> 10: 0078 bc00 0000 1c40 0c68 0003 0000 0000
> 18: 41ff 0000 000a 9088 0000 0000 0000 0000

Ah, thanks for catching this.

> It's advertising pause + asym pause, 1000BASE-T FD, link partner is also
> advertising 1000BASE-T FD but no pause abilities.
>
> When comparing this with a Marvell 88e1111:
>
> 00: 1140 7949 0141 0cc2 05e1 0000 0004 2001
> 08: 0000 0e00 4000 0000 0000 0000 0000 f000
> 10: 0078 8100 0000 0040 0568 0000 0000 0000
> 18: 4100 0000 0002 8084 0000 0000 0000 0000
>
> It looks remarkably similar. However, The first few reads seem to be
> corrupted with 0x01ff. It may be that the module is slow to allow the
> PHY to start responding - we've had similar with Champion One SFPs.

Do you have an an example of how to work around this? Even reading one
register at a time I still get the bogus 0x01ff. Reading bytewise, a
reasonable-looking upper byte is returned every other read, but the
lower byte is 0xff every time.

> It looks like it's a Marvell 88e1111. The register at 0x11 is the
> Marvell status register, and 0xbc00 indicates 1000Mbit, FD, AN
> resolved, link up which agrees with what's in the various other
> registers.

That matches some supplemental info on the manufacturer's website (which
was frustratingly not associated with the model number of this
particular module).

--Sean