Re: [PATCH v3 0/2] i2c: imx: fix SMBus block-read of 0 locking the bus [stable backport question/offer]

[Dominique Martinet <asmadeus@codewreck.org>]

Vincent Jardin wrote on Mon, Jul 13, 2026 at 08:11:58PM +0200:
> i2c-imx rejects an SMBus Block Read byte count of 0 (valid per SMBus 3.1
> 6.5.7) as -EPROTO and returns without emitting a NACK + STOP, leaving the
> target holding SDA so the bus stays stuck until a power cycle.
> 
> It was triggered by an MPQ8785 PMBus regulator on a LX2160A i2c
> bus: when the kernel binds it using the pmbus/hwmon framework, the bus
> locks up and it does never recovers. It was confirmed with a scope, with
> and without the fix.
> 
> The same bug is occuring with two independently introduced spots, so the
> fix is two patches with their respective Fixes: tags and backport ranges
> 
>   1/2  atomic/polling path       Fixes: 8e8782c71595   v3.16+
>   2/2  IRQ-driven state machine  Fixes: 5f5c2d4579ca   v6.13+

Silly question (half for stable people, half for i2c-imx maintainers),
but the backport for commit cb2fc3785769 ("i2c: imx: fix locked bus on
SMBus block-read of 0 (atomic)") to stable brought in b460b15b3cc2
("i2c: imx: separate atomic, dma and non-dma use case") (also 6.13+) as
a dep (all the way back to 5.10!);
with that commit in, 5f5c2d4579ca ("i2c: imx: prevent rescheduling in non
dma mode") applies almost cleanly on 6.6/6.12[1]... So should we grab
more easy fixes?
In particular, I doubt I'll ever hit this SMBus 3.1 bug, but
5f5c2d4579ca also was a real fix[2], so would it make sense to jump in
and get both 5f5c2d4579ca and 07fd9385f0d8 ("i2c: imx: fix locked bus on
SMBus block-read of 0 (IRQ)") for 6.6/6.12?

[1] just a trivial context conflict in the struct there, but it starts
being more iffy on 6.1 and earlier kernels
[2] ... We actually ran into that bug on 5.10, our kludgy backport being
the reason I noticed during today's 5.10.266-rc1 testing...


Honestly, I wouldn't have considered backporting either as b460b15b3cc2
("i2c: imx: separate atomic, dma and non-dma use case") looks too big to
backport to me, so I definitely wouldn't have done it before, but that
ship has sailed (it's in the 5.10 -rc right now, but it's been merged a
couple of weeks ago in higher versions stables), so at this point I
don't think it's worth reverting either and we might as well keep
falling forward...



tl;dr: If maintainers agree, I can send these two for a future 6.6/6.12:
5f5c2d4579ca ("i2c: imx: prevent rescheduling in non dma mode")
07fd9385f0d8 ("i2c: imx: fix locked bus on SMBus block-read of 0 (IRQ)")


Thanks,
-- 
Dominique Martinet | Asmadeus