linux-kernel - Re: [PATCH 2/2] net: sfp: support 25G long-range modules (extended compliance code 0x3)

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Message-ID: <a8ea329c-42b9-4adc-80ad-2f602a5fbf0c@solid-run.com>
Date: Mon, 19 Jan 2026 07:30:20 +0000
From: Josua Mayer <josua@...id-run.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Heiner Kallweit <hkallweit1@...il.com>, Russell King
	<linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Mikhail Anikin
	<mikhail.anikin@...id-run.com>, Rabeeh Khoury <rabeeh@...id-run.com>, Yazan
 Shhady <yazan.shhady@...id-run.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] net: sfp: support 25G long-range modules (extended
 compliance code 0x3)

On 18/01/2026 18:01, Andrew Lunn wrote:
> On Sun, Jan 18, 2026 at 04:07:38PM +0200, Josua Mayer wrote:
>> The extended compliance code value SFF8024_ECC_100GBASE_ER4_25GBASE_ER
>> (0x3) means either 4-lane 100G or single lane 25G.
> Is there a way to tell them apart?
The physical connectors are different, so we can know from the
device-tree compatible string.

For now sfp driver does not support qsfp.

>
> If it is a QSFP, it means 4-lane 100G?
This is my suspicion, but I have not parsed real-world qsfp eeproms.
> You can however split it into
> 4x 25GBASE_ER, if the MAC supports port spitting? If it is an SFP, it
> must mean 25GBASE_ER because the SFP only supports a single lane?
Does it?
I thought SR, ER and LR indicate distance not host interface lane count.

Either way if you have a QSFP module, there is a single module with a single
eeprom on a single connector of 4 lanes.

When you have SFP module, there is a module / eeprom for each lane.

>
>> Set 25000baseLR_Full mode supported in addition to the already set
>> 100000baseLR4_ER4_Full, and handle it in sfp_select_interface.
>>
>> This fixes detection of 25G capability for two SFP fiber modules:
>>
>> - GigaLight GSS-SPO250-LRT
>> - FS SFP-25G23-BX20-I
> Are these SFPs or QSFPs?

SFP.

>
>> Signed-off-by: Josua Mayer <josua@...id-run.com>
>> ---
>>   drivers/net/phy/sfp-bus.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/phy/sfp-bus.c b/drivers/net/phy/sfp-bus.c
>> index b945d75966d5..2caa0e0c4ec8 100644
>> --- a/drivers/net/phy/sfp-bus.c
>> +++ b/drivers/net/phy/sfp-bus.c
>> @@ -247,6 +247,7 @@ static void sfp_module_parse_support(struct sfp_bus *bus,
>>   	case SFF8024_ECC_100GBASE_LR4_25GBASE_LR:
>>   	case SFF8024_ECC_100GBASE_ER4_25GBASE_ER:
>>   		phylink_set(modes, 100000baseLR4_ER4_Full);
>> +		phylink_set(modes, 25000baseLR_Full);
> Given the question above, i'm wondering if it is as simple as this, or
> we need to look at the type of SFP?
I don't think we need to worry about QSFP at this time.