Re: [PATCH v10 0/7] I2C Mux per channel bus speed

[Andy Shevchenko]

On Wed, Jul 08, 2026 at 02:16:12PM +0200, Marcus Folkesson wrote:
> This was a RFC on how to implement a feature to have different bus
> speeds on different channels with an I2C multiplexer/switch.
> As no major complaints on the design came up during the review, I
> decided to submit the series without the RFC tag.
> 
> The benefit with this feature is that you may group devices after
> the fastest bus speed they can handle.
> A real-world example is that you could have e.g. a display running @400kHz
> and a smart battery running @100kHz using the same I2C controller.
> 
> There are many corner cases where this may cause a problem for some
> hardware topologies. I've tried to describe those I could think of
> in the documentation, see Patch #5.
> 
> E.g. one risk is that if the mux driver does not disconnect channels
> when Idle, this may cause a higher frequency to "leak" through to
> devices that are supposed to run at lower bus speed.
> This is not only a "problem" for changing bus speed but could also be
> an issue for potential address conflicts.
> 
> This patchset has been used and tested heavily the last months
> on a custom board based on a da850 (DaVinci) platform.

...

> Changes in v10:
> 
> - Fix gramatics in documentation
> - Move {__,}i2c_adapter_set_clk_freq() to i2c-mux.c

Can you point to the discussion where it was suggested, please?
It was like ages ago (too many patches to review) and I probably
missed and/or forgot the rationale for that. Also if we move
to i2c-mux, why do we leave it in the adapter namespace?

> - Make set_clk_freq() return actual frequency
> - Reimplement idle_state (from earlier version)
> - Implement example on idle_state for ltc4306
> - Link to v9: https://lore.kernel.org/r/20260324-i2c-mux-v9-0-5292b0608243@xxxxxxxxx

FWIW, I briefly read the v9 discussion and haven't got the above move,
seems wasn't discussed there?

-- 
With Best Regards,
Andy Shevchenko