Re: [PATCH v4 9/9] i2c: atr: add passthrough flag

[Romain Gantois <romain.gantois@bootlin.com>]

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On Monday, 28 April 2025 12:25:14 CEST Cosmin Tanislav wrote:
> Some I2C ATRs can have other I2C ATRs as children. The I2C messages of
> the child ATRs need to be forwarded as-is if the parent I2C ATR can
> only do static mapping.
> 
> In the case of GMSL, the deserializer I2C ATR actually doesn't have I2C
> address remapping hardware capabilities, but it is able to select which
> GMSL link to talk to, allowing it to change the address of the
> serializer.
> 
> The child ATRs need to have their alias pools defined in such a way to
> prevent overlapping addresses between them, but there's no way around
> this without orchestration between multiple ATR instances.
> 
> To allow for this use-case, add a flag that allows unmapped addresses
> to be passed through, since they are already remapped by the child ATRs.
> 
> There's no case where an address that has not been remapped by the child
> ATR will hit the parent ATR.
> 
> Signed-off-by: Cosmin Tanislav <demonsingur@gmail.com>
> ---
>  drivers/i2c/i2c-atr.c   | 7 +++++--
>  include/linux/i2c-atr.h | 2 ++
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-atr.c b/drivers/i2c/i2c-atr.c
> index 721dd680f2ac..eccb85c34609 100644
> --- a/drivers/i2c/i2c-atr.c
> +++ b/drivers/i2c/i2c-atr.c
> @@ -394,6 +394,9 @@ static int i2c_atr_map_msgs(struct i2c_atr_chan *chan,
> struct i2c_msg *msgs, c2a = i2c_atr_get_mapping_by_addr(chan,
> msgs[i].addr);
> 
>  		if (!c2a) {
> +			if (atr->flags & I2C_ATR_F_PASSTHROUGH)
> +				continue;
> +
>  			dev_err(atr->dev, "client 0x%02x not mapped!\n",
>  				msgs[i].addr);
> 
> @@ -486,13 +489,13 @@ static int i2c_atr_smbus_xfer(struct i2c_adapter
> *adap, u16 addr,
> 
>  	c2a = i2c_atr_get_mapping_by_addr(chan, addr);
> 
> -	if (!c2a) {
> +	if (!c2a && !(atr->flags & I2C_ATR_F_PASSTHROUGH)) {
>  		dev_err(atr->dev, "client 0x%02x not mapped!\n", addr);
>  		mutex_unlock(&chan->alias_pairs_lock);
>  		return -ENXIO;
>  	}
> 
> -	alias = c2a->alias;
> +	alias = c2a ? c2a->alias : addr;
> 
>  	mutex_unlock(&chan->alias_pairs_lock);
> 
> diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
> index 7c6a9627191d..f979b931ca05 100644
> --- a/include/linux/i2c-atr.h
> +++ b/include/linux/i2c-atr.h
> @@ -22,9 +22,11 @@ struct i2c_atr;
>   * enum i2c_atr_flags - Flags for an I2C ATR driver
>   *
>   * @I2C_ATR_F_STATIC: ATR does not support dynamic mapping, use static
> mapping + * @I2C_ATR_F_PASSTHROUGH: Allow unmapped incoming addresses to
> pass through */
>  enum i2c_atr_flags {
>  	I2C_ATR_F_STATIC = BIT(0),
> +	I2C_ATR_F_PASSTHROUGH = BIT(1),
>  };
> 
>  /**

Reviewed-by: Romain Gantois <romain.gantois@bootlin.com>

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