Re: [PATCH v2 9/9] i2c: atr: add passthrough flag

Romain Gantois
2025-02-27T14:03:13Z

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On mardi 25 février 2025 12:39:37 heure normale d’Europe centrale 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 | 3 +++
> include/linux/i2c-atr.h | 2 ++
> 2 files changed, 5 insertions(+)
>
> diff --git a/drivers/i2c/i2c-atr.c b/drivers/i2c/i2c-atr.c
> index f7b853f55630..1986fa055f20 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_PASSTHROUGH)
> + continue;

Shouldn't this check also be added to i2c_atr_smbus_xfer?

> +
> dev_err(atr->dev, "client 0x%02x not mapped!\n",
> msgs[i].addr);
>
> diff --git a/include/linux/i2c-atr.h b/include/linux/i2c-atr.h
> index 2f79d0d9140f..b3797a930a7a 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_STATIC: ATR does not support dynamic mapping, use static
> mapping + * @I2C_ATR_PASSTHROUGH: Allow unmapped incoming addresses to pass
> through */
> enum i2c_atr_flags {
> I2C_ATR_STATIC = BIT(0),
> + I2C_ATR_PASSTHROUGH = BIT(1),

As stated for the previous patch, I'd prefer the "I2C_ATR_F_*" naming
convention.

Thanks,

--
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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