Re: [PATCH v12 2/7] i2c: mux: add idle_state property to i2c_mux_core

[Peter Rosin]

Hi!

On 2026-07-19 16:59, Marcus Folkesson wrote:
> Muxes treat their channels differently when idle.
> Let the mux core have this information to make it available for
> internal use.
> 
> Possible idle states are:
>   - I2C_MUX_IDLE_AS_IS: Leave channels as is when idle
>   - I2C_MUX_IDLE_DISCONNECT: Disconnect channel (set HiZ when idle)
>   - I2C_MUX_IDLE_UNKNOWN: Unknown idle state
>   - <n>: Enable channel n (starting from 0) when idle"
> 
> Default value is set to I2C_MUX_IDLE_UNKNOWN.
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> Signed-off-by: Marcus Folkesson <marcus.folkesson@xxxxxxxxx>
> ---
>   drivers/i2c/i2c-mux.c   |  1 +
>   include/linux/i2c-mux.h | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 31 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index 681a201c239b..b126ce7338c2 100644
> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -247,6 +247,7 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
>   	muxc->select = select;
>   	muxc->deselect = deselect;
>   	muxc->max_adapters = max_adapters;
> +	muxc->idle_state = I2C_MUX_IDLE_UNKNOWN;
>   
>   	return muxc;
>   }
> diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
> index 1784ac7afb11..a348f81e7a90 100644
> --- a/include/linux/i2c-mux.h
> +++ b/include/linux/i2c-mux.h
> @@ -15,6 +15,10 @@
>   
>   #include <linux/bitops.h>
>   
> +#define I2C_MUX_IDLE_AS_IS      (-1)
> +#define I2C_MUX_IDLE_DISCONNECT (-2)
> +#define I2C_MUX_IDLE_UNKNOWN	(-3)
> +
>   struct i2c_mux_core {
>   	struct i2c_adapter *parent;
>   	struct device *dev;
> @@ -22,6 +26,18 @@ struct i2c_mux_core {
>   	unsigned int arbitrator:1;
>   	unsigned int gate:1;
>   
> +	/*
> +	 * The mux state used by the driver when idle.
> +	 * Possible idle states are:
> +	 *  - I2C_MUX_IDLE_AS_IS: Leave channels as is when idle
> +	 *  - I2C_MUX_IDLE_DISCONNECT: Disconnect channel (set HiZ when idle)
> +	 *  - I2C_MUX_IDLE_UNKNOWN: Unknown idle state
> +	 *  - <n>: Enable channel n (starting from 0) when idle"
> +	 *
> +	 * Default value is set to I2C_MUX_IDLE_UNKNOWN.
> +	 */
> +	int idle_state;
> +
>   	void *priv;
>   
>   	int (*select)(struct i2c_mux_core *, u32 chan_id);
> @@ -38,6 +54,20 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
>   				   int (*select)(struct i2c_mux_core *, u32),
>   				   int (*deselect)(struct i2c_mux_core *, u32));
>   
> +/*
> + * Mux drivers may only change idle_state, and may only do so
> + * between allocation and registration of the mux controller.

This is simply not true. It is a limitation imposed by your series.
The pca954x driver has a hook to change the idle state at runtime
(the change takes effect the next time the mux is deselected).

Cheers,
Peter

> + */
> +static inline void i2c_mux_set_idle_state(struct i2c_mux_core *muxc, int state)
> +{
> +	muxc->idle_state = state;
> +}
> +
> +static inline int i2c_mux_idle_state(struct i2c_mux_core *muxc)
> +{
> +	return muxc->idle_state;
> +}
> +
>   /* flags for i2c_mux_alloc */
>   #define I2C_MUX_LOCKED     BIT(0)
>   #define I2C_MUX_ARBITRATOR BIT(1)
>