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

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Message-ID: <3833744.MHq7AAxBmi@fw-rgant>
Date: Thu, 27 Feb 2025 15:03:11 +0100
From: Romain Gantois <romain.gantois@...tlin.com>
To: Cosmin Tanislav <demonsingur@...il.com>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>, linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, Cosmin Tanislav <demonsingur@...il.com>
Subject: Re: [PATCH v2 9/9] i2c: atr: add passthrough flag

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@...il.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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