Subject: Re: [PATCH net-next v9 1/3] net: sfp: initialize i2c_block_size at adapter configure time

From: Jakub Kicinski <[email-masked]>
Date: Wed, 3 Jun 2026 18:06:07 -0700

On Thu, 28 May 2026 20:52:40 +0000 Jonas Jelonek wrote:
> sfp->i2c_block_size is only assigned in sfp_sm_mod_probe(), which runs
> from the state machine timer after SFP_F_PRESENT has been set. Between
> those two points, sfp_module_eeprom() (the ethtool -m callback) gates
> only on SFP_F_PRESENT and can be entered with i2c_block_size still at
> its kzalloc'd value of 0.
> 
> On a pure-I2C adapter, sfp_i2c_read() then issues an i2c_transfer()
> with msgs[1].len = 0 inside a loop that subtracts this_len from len
> each iteration; on adapters that succeed a zero-length read the loop
> never advances, spinning while holding rtnl_lock.
> 
> This was previously addressed by initializing i2c_block_size in
> sfp_alloc() (commit 813c2dd78618), but the initialization was dropped
> when i2c_block_size was split from i2c_max_block_size.
> 
> Initialize sfp->i2c_block_size from sfp->i2c_max_block_size in
> sfp_i2c_configure(), so the field is valid as soon as the adapter is
> known. sfp_sm_mod_probe() still reassigns it on each module insertion
> to recover from a per-module clamp to 1 (sfp_id_needs_byte_io).
> 
> Fixes: 7662abf4db94 ("net: phy: sfp: Add support for SMBus module access")
> Cc: [email-masked]
> Signed-off-by: Jonas Jelonek <[email-masked]>

Thanks for splitting this out.
This is a fix it needs to take the net/Linus route rather than the
net-next route. I'll apply just patch 1 and you'll have to repost
patches 2 and 3 on Friday.

In the meantime - AI seems to also be saying something the cap being
potentially off by 1 in patch 2? We add 1 to the len? Maybe I'm
misunderstanding..

https://sashiko.dev/#/patchset/[email-masked]