linux-kernel - Re: [PATCH v2 0/5] I2C Mux per channel bus speed

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Message-ID: <aO5afkSgjvDViMId@gmail.com>
Date: Tue, 14 Oct 2025 16:13:18 +0200
From: Marcus Folkesson <marcus.folkesson@...il.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>,
	Peter Rosin <peda@...ntia.se>,
	Michael Hennerich <michael.hennerich@...log.com>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Andi Shyti <andi.shyti@...nel.org>
Cc: linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 0/5] I2C Mux per channel bus speed

Hi all,

On Thu, Oct 02, 2025 at 04:41:31PM +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.
> 
> The implementation is split up into several patches:
> 
> Patch #1 Introduce a callback for the i2c controller to set bus speed
> Patch #2 Introduce functionality to adjust bus speed depending on mux
>          channel.
> Patch #3 Cleanup i2c-davinci driver a bit to prepare it for set_clk_freq
> Parch #4 Implement set_clk_freq for the i2c-davinci driver
> Parch #5 Update documentation with this feature

Any more comments on this series?

Thanks,
Marcus Folkesson


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