netdev - Re: [PATCH net-next v5] net: sfp: extend SMBus support

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Message-ID: <91442f3f-0da9-4c52-89ce-2ca0a3188836@gmail.com>
Date: Sun, 18 Jan 2026 10:43:12 +0100
From: Jonas Jelonek <jelonek.jonas@...il.com>
To: Andrew Lunn <andrew@...n.ch>,
 Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Russell King <linux@...linux.org.uk>,
 Heiner Kallweit <hkallweit1@...il.com>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Bjørn Mork <bjorn@...k.no>
Subject: Re: [PATCH net-next v5] net: sfp: extend SMBus support

Hi,

On 16.01.26 15:25, Andrew Lunn wrote:
>> But let's first figure-out if word-only smbus are really a thing
> Some grep foo on /drivers/i2c/busses might answer that.

Did that and haven't found any driver in mainline which is word-only.
All drivers with word access capability have byte access too.

FWIW, I briefly looked at some specifications. SMBus doesn't seem
to require any hierarchy or bare minimum operations, so it's up to the
vendor which operations are implemented. Though one could argue,
byte access is probably simpler to implement and if a vendor implements
word access, byte access is usually implemented too.

Looking at the SFP MSA [1], some sentences sound like one could assume
byte access is needed at least for SFP. In Section B4, there are statements
like:
- "The memories are organized as a series of 8-bit data words that can be
    addressed individually..."
- "...provides sequential or random access to 8 bit parameters..."
- "The protocol ... sequentially transmits one or more 8-bit bytes..."

But that may be too vague and I can't judge if that's a valid argument to not
care about word-only here.

Kind regards,
Jonas

[1] https://members.snia.org/document/dl/26184