[PATCH] i2c: mux: Fix the crash when the i2c-arbitrator node is present

[Heiko Schocher]

Hello Venkatesh,

On 28.05.25 05:12, Venkatesh Yadav Abbarapu wrote:
> Observing the crash when we add the i2c-arbitrator node in the device

Which crash?

> tree as per the DT bindings. The issue is with the child node of
> i2c-arbitrator at 72 i.e., i2c at f1950000->i2c-arbitrator at 72->i2c-arb, as the
> arbitrator uses the uclass of mux(UCLASS_I2C_MUX) and the mux uclass driver
> checks for the "reg" property using the i2c_mux_child_post_bind() function,
> if it won't find the "reg" property it will return -EINVAL which is leading
> to the crash.
> So, add the logic to check whether the  child node has the "reg" property,
> if the "reg" property exists then read the "reg" and update the channel.
> 
> https://www.kernel.org/doc/Documentation/devicetree/bindings/i2c/i2c-arb.txt
> 
> Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu at amd.com>
> ---
>   drivers/i2c/muxes/i2c-mux-uclass.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-uclass.c b/drivers/i2c/muxes/i2c-mux-uclass.c
> index d1999d21feb..b18999c1fe3 100644
> --- a/drivers/i2c/muxes/i2c-mux-uclass.c
> +++ b/drivers/i2c/muxes/i2c-mux-uclass.c
> @@ -40,11 +40,14 @@ static int i2c_mux_child_post_bind(struct udevice *dev)
>   	struct i2c_mux_bus *plat = dev_get_parent_plat(dev);
>   	int channel;
>   
> -	channel = dev_read_u32_default(dev, "reg", -1);

Shouldn;t this function return -1 (the default value), if property "reg" is
not present? (And also if dev_ofnode(dev) is not valid?)

Seems we should look into this function and may fix the problem there?

Aha, this comes from

drivers/core/read.c
int dev_read_u32_default(const struct udevice *dev, const char *propname,
                          int def)
{
         return ofnode_read_u32_default(dev_ofnode(dev), propname, def);
}

with drivers/core/ofnode.c
u32 ofnode_read_u32_default(ofnode node, const char *propname, u32 def)
{
         assert(ofnode_valid(node));
         ofnode_read_u32_index(node, propname, 0, &def);

         return def;
}

added Simon.

@Simon: may proper fix would be to check in ofnode_read_u32_default()
         if propname exists, and if not return default value?
         May also return with default value if node is not valid?

         What do you think?

         Thanks!


> -	if (channel < 0)
> -		return -EINVAL;
> -	plat->channel = channel;
> +	ofnode node = dev_ofnode(dev);
>   
> +	if (ofnode_has_property(node, "reg")) {

If we fix it in this code, you can here simply return immediately
if "reg" propertyis missing, so you can save the identation level,
and patch looks cleaner.

> +		channel = dev_read_u32_default(dev, "reg", -1);
> +		if (channel < 0)
> +			return -EINVAL;
> +		plat->channel = channel;
> +	}
>   	return 0;
>   }
>   
> 

Thanks!

bye,
Heiko
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