Re: [PATCH v2 1/7] i3c: renesas: Fix zero I2C SCL rate on pure I3C buses

[Frank Li]

On Mon, Oct 26, 2026 at 11:35:44AM +0000, Diogo Ivo wrote:
> On a pure I3C bus there are no I2C devices, so the I3C core leaves
> bus->scl_rate.i2c at zero if i2c-scl-hz is not specified in DT.
> Deriving i2c_total_ticks from that zero rate programs a zero-width
> open-drain SCL into the STDBR open-drain fields, which are still used
> in pure I3C mode for example in DAA.
>
> Fall back to the 1 MHz FM+ limit instead, the fastest rate an I2C
> device could have, so that a sane open-drain timing is programmed.
>
> Fixes: d028219a9f14 ("i3c: master: Add basic driver for the Renesas I3C controller")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Diogo Ivo <diogo.ivo.sx@xxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

> Changes in v2:
>  - Substituted if/else with ternary operator
>  - Picked up R-b from Wolfram Sang
> ---
>  drivers/i3c/master/renesas-i3c.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i3c/master/renesas-i3c.c b/drivers/i3c/master/renesas-i3c.c
> index 8b264f72e55c..78d0a2c4a19e 100644
> --- a/drivers/i3c/master/renesas-i3c.c
> +++ b/drivers/i3c/master/renesas-i3c.c
> @@ -579,7 +579,15 @@ static int renesas_i3c_bus_init(struct i3c_master_controller *m)
>  	if (!i3c->rate)
>  		return -EINVAL;
>
> -	i2c_total_ticks = DIV_ROUND_UP(i3c->rate, bus->scl_rate.i2c);
> +	/*
> +	 * A pure I3C bus has no I2C devices, so the I3C core leaves
> +	 * scl_rate.i2c at zero if not explicitly defined in DT. The
> +	 * open-drain SCL fields of STDBR, which are used for the DAA
> +	 * pending read, are derived from it though, so fall back to
> +	 * the 1 MHz FM+ limit instead of programming a zero-width clock.
> +	 */
> +	i2c_total_ticks = DIV_ROUND_UP(i3c->rate,
> +				       bus->scl_rate.i2c ?: I3C_BUS_I2C_FM_PLUS_SCL_MAX_RATE);
>  	i3c_total_ticks = DIV_ROUND_UP(i3c->rate, bus->scl_rate.i3c);
>
>  	i2c_parse_fw_timings(&m->dev, &t, true);
>
> --
> 2.56.0
>